OK, then you should need to modify the service menu. The way to enter is by pressing 0 6 2 5 9 6 and then the i+ key on your remote.
You should see the main service menu screen. Move to "alignments" and then to Geo-Nor / Geo-SW / Geo 4:3 / Geo 100 HZ (the most important is Geo-Nor ). DO NOT CHANGE ANYTHING YET. WRITE DOWN ALL THE VALUES THAT APPEAR IN THE DIFFERENT FIELDS IN CASE YOU NEED TO RESTORE THEM (PROBABLY). Now you are ready to modify the geometry: to do that you will need some kind of test patterns with reference images; I use "Digital Video Essentials" (easy to buy on-line). Now is a matter of trying different values. I think you should modify the parameters Upper/lower eastwest corner, but it depends on the nature of your fault. Be aware that horizontal bending can hardly be solved in the service menu, but you can improve it a little.
By the way, prepare some time in complete quietness. You will notice that you will need it.
Once finished, do not forget to store the changes in the main menu and press the menu key to exit.
Regards,