Razor Blade Utility Knife for starters to cut the paint if it were I. Then you need to determine if there is a heavy buildup at the edge sash to pinch it in the frame.

Here is a picture of the sash and the tools I have tried so far

Hyde 45200 Window Zipper, fastest easiest way to open them.

Here's the problem: it's not just the paint you see but the paint that seeped in between the sash and the frame. That dried paint is just like glue. So, after you finish removing all the visible paint, you will have to go after the rest of the paint that isn't on the exterior. That is going to involve using a multi-max reciprocating blade and/or maybe a really thin-bladed joint compound knife. If that doesn't work, you may have to consider taking the sash apart. Expect some damage....