How do one adjust the convergence?

My RCA projection television works fine except the screen convergence. It bow inward at the center. Went through the adjustment process in manual. Can't get the bow out! Helppp!

Model Number p52960, p61960 date 06/18/01

How can the convergence be adjusted to show picuture without the bow at the center?
Maybe back to factory veiwing. It was showing good, than all of a sudden it bowed. I perform the adjustment in my manual. It made the picture better, but the bow is still there. At the bottom of the screen, the picture doesn't fit the screen.