It may not be the regulators. The window could be binding up in the door due to the original channel being worn or missing. Remove the steel inspection panel on the doors and unscrew the regulator which will allow the window and regulator to drop down where you can see the regulator. The regulator will slide off the glass track and you can remove it for inspection. If you need to remove the glass to replace the the channel the glass comes out through to opening at the top of the door. While you are at it you might want to remove the door latch mechanism and clean and lube it also.