There’s no need to bust out a window to remove it. I know I have seen people that do this. It does nothing more than make a bigger mess than needed.
The best way to do this is to remove the framing around the window. You know this, it’s the wood or molding that goes around the outside on the wall itself.
Once you carefully remove the molding, you will be able to see the cracks between the window and the wall joist.
If the window doesn’t want to leave freely from it’s place, taking a crowbar or something similar to pry it lose could help. Just be careful.
Once you have it lose, you can safely remove the window and place it aside. Probably be best if outside.
If there is any sealant or glue on the wall frame, sanding it off will help insure the other window doesn’t have problems going in.
Then once you have that done you can bring in the new window and make sure the measurements are accurate.
If it fits, then placing a sealant/glue on the framing, all the way around, will allow you to seal it and no longer worry about drafts.
Once you have that sealed, you can now carefully replace the molding back around the window.
TaDa you just install a window.