Most pocket doors have two rollers mounted to the top of the door that hold the wheels that ride in a track/channel. The "bolt" that connects the door to the wheels should have an adjustment nut that you can use to bring the door up or down and these can be used to adjust the door. In the "best case" you need the special little wrench that comes with the door hardware that is thin enough to slip up there. These are a 25 cent item that you will probably have to ask your local hardware store manager to sneak one out of the package for you to use, since I don't think you can buy them. Worst case, the wooden trim was brought down so far on the header that you can't access it and you need to remove it first. You shouldn't have to remove the door, or make sure anything is perfectly level. What matters is that the door hits the jamb in a parallel manner. In your case, it sounds like you need to adjust the roller on the striking side of the door so the door comes up on that side. This will bring the bottom of the leading edge of the door closer to the jamb and make the door parallel to the jamb. If you can't do this, then adjust the other roller so the trailing edge goes down.