No, you can only use 12 gauge wire with a 20 amp circuit, even if it's just for lights. You would have to replace the existing 14 gauge wire with 12 gauge to upsize the breaker.

While probably beyond your skill level, you might want to think about adding a couple of more 20 amp circuits for your garage/workshop. Ideally you want your lights on a different circuit than your tools. You really don't want to be standing in the dark with your fingers close to a table saw blade as it spins down.

Get a couple or three estimates from licensed electricians in your area. The new circuits will be a lot cheaper than a trip to the emergency room.

Is this a garage that is detached from the house?

It is a detached garage. There is an underground pvc pipe run from the house to the garage in order to run additional wire though.

How far is the garage from the main box? The reason I'm asking is that maybe the larger wire size was used to minimize the voltage drop. So even if you switched everything out to 12 gauge, you might not be able to change the breaker to 20A.

Distance matters.

Good thought. The distance is about 20-25 feet.

Okay, then that's not the reason. :)

Are you sure that a 20A circuit would be enough? Or do you need to run another (shared neutral) circuit or install a subpanel in the garage?

Is your main panel a fuse panel?

Just curious, because you say "blowing breakers" which doesn't really make sense. But then say fuse panel later on. I'm assuming you meant 'blowing fuses'.

Tripping breakers.

So when you said 'fuse panel', you meant breaker panel?

Is there room in it for more circuits?

And when you say "main receptacle in the garage" are you just referring to the first duplex receptacle or are you meaning something else entirely?

It may seem like I'm nitpicking but I just want to make sure we're all on the same page so that we can advise you properly and getting the right terminology is the first step.

There is room for more circuits. Probably 8 available spots. I have 100 amp service to the house.

Then I guess your options are:

Easy but maybe not good enough - Switch out all of the 14 gauge wire to 12 gauge and change the 15A breaker to 20A.

A little harder, but probably good enough - Change the single circuit feeding the garage into a shared neutral circuit. This essentially adds a whole new circuit, but you'll have to run another hot wire through the conduit (you'll probably have to pull the existing wires out and then pull all of them back in). Then you'd add a double breaker to your panel with one hot on each breaker.

You can only have one circuit feeding an out building, and a shared neutral circuit is considered a single circuit.

This will give you double what you have now.

Probably overkill - Install a subpanel and feed it appropriately

Run a larger 240 volt wire from house to garage workshop place. Terminate this new wire into a subpanel MAIN LUG breaker panel. Have the original #14 gauge light wiring on there own 15 amp 120 volt breaker (single pole) in this subpanel. Run each piece of motor load on its own 20 amp 120 volt breakers (single pole). The reason for this is start up on any motor is the largest amperage draw. By doing this you can turn on anything your heart desires all at once and not blow anything in the process. Contact me and I will help you figure the wattage required for the 240 volt subpanel wiring D B Electric elecwired@live.com

D&B's suggestion isn't a bad one but note that you probably escaped having a grounding system (rods, for example) in the detached garage before. Putting in a subpanel will require you to do so.

As mentioned, even if the breaker doesn't blow, long runs of smaller wire can result in a voltage drop that can keep a lot of motors such as table saws from starting properly (been there done that).

Hello Ron Natalie the grounding conductors can be pulled thru the same conduit or 240 volt subpanel cable type that attaches to the breaker controlling this new wire from the Main Breaker panel source to the workshop. Check with your local authority before adding extra grounding rod or rods as some locations require a looped grounding from one source only to all Main Breaker and up to 6 subpanel locations. The subpanel to the workshop may seem like over kill but none of the motors will be lagging from to small of a wire trying to feed it all now. By adding individual breakers to the original wiring it separates the loads for the proper wire gauge to the proper circuit breaker size www.dbelectric.us

While the local authority is obviously going to dictate, pulling grounds to an accessory structure under the NEC is ***NOT SUFFICIENT*** grounding for a structure with more than one circuit. It is however now required (under the last two NEC revisions) to pull the ground between the structures ****IN ADDITION*** to having the grounding electrodes at the second structure (there used to be an exception for structures not connected with some other metallic connection).

Your garage has a separate panel correct? What is the main breaker for said panel so we know. Also it sounds like you need more sufficient wiring for the outlets, two or three more GFCI 20A circuits. Table saw will want its own circuit, it pulls 13 or more Amps by itself. And as Ron notes, you need a separate ground for the garage as well.

Welcome to the rabbit hole