Overgrown?

If you mean 'leggy' because of lack of sunlight, you can give them a trim with secateurs or scissors. Don't take more than one-third of total growth on each plant.

The prunings can be used for drying. You can collect them up and tie them into small bundles, but it's probably easier to just spread them out onto some paper towelling on a rack and leave them to air dry. Once dry, use finger and thumb to strip the leaves off the stems. Easy peasy.

I just got through pruning ALL my mints. I grabbed bunches of their stalks and hacked at probably the top 2/3's of them. In no time at all, new sprouts will appear and the garden will be fresh with new mint.

Fresh mint, by far, is better than dried mint any day. Try and use fresh when you can. During it's growing season(depending on where you are), that can be a long time. Fresh beats dried hands down. Dried will do in a pinch, but only when there's no other alternative.

I agree 100%. With mint, fresh is far superior. I don't think it holds its flavour or aroma at all when dried. Freeze it instead, if you have to store it. Try putting some in water or fruit juice in ice cube containers, or flatten it out into a thin pancake (make layers separated with plastic wrap) so you can break of bits as required.