Since you haven't supplied the model, I'll guess that it is something like a G223. You should see a metal plate in front of the printer ( usually has an arrow on it). Lift it slightly then pull it forward and out. The roller is clipped into it. Fit the new roller and clip it back into the register.
If anyone has trouble finding JCM Gold programming manuals, C-tech has them here:
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cash registers.