It sounds like you've got a "Narrow Line Double Hung". To get to the Balancers, you will need to take the upper and lower sash out. (The sash are the frames of glass that move).
If you look at the left side of the window , from the inside, and half way between the top and bottom you'll see a split in the Vinyl Jamb Liner. There will be 5-6 aluminum screws on the liner below the split. Take all the screws out (you'll have to pull down the upper sash all the way to get to the last screw). Push both sash all the way up. Grab the lower jamb liner and pull down and out. (You're trying to pull the liner out from behind the sash WITHOUT bending the vinyl liner). Pull the lower sash down and you'll see it can now be removed. Watch out for the cord that connects to the sash, it will have alot of tension, so make sure you have a good grip on the cord when you remove it from the sash. Do the same thing for the top sash. Pull the top side jamb liner out, no screws. The balancers are located under the "Head Jamb Liner", you'll have three aluminum screws to remove.
If you don't have a replacement balancer you'll need to talk to your local Andersen dealer that is part of the "Dealer Service Network" or to Andersen service at (888) 888 7020

Best of luck...

Here is a link that might be useful: Sash Replacement for double-hung windows 1962 to present

Double Hung Window, CIG-2, 1-89

How do I order and replace the seal which is under the window sill?