Yeah Mylenium is correct. Photoshop can create the UV texture, but has no way of really altering the UV map. It just received a new feature for UV's but I have not tested it yet nor would it help in this situation. But at least they are/or were working on UV issues. I guess we will see what the next update brings.
Most 3d apps provide ways to alter the map so it may be worth your time to real the manual for that app.
Also UV Mapper is a nice alternative, not sure it will do everything you need, but at least it can do basic editing. (I think it works on obj files only. It's been awhile.)