Do I have to get a new eye prescription to get glasses every time I want new glasses?

Depends. If your vision has changed since the last time you got glasses, you'll certainly want to be examined to get a new prescription. If you just want a different style frame/lens shape, the glasses providers can read your prescription from current glasses & adapt it to new frames /lenses of your choice. Still a good idea to have yearly eye exam to check for glaucoma, cataracts, macular degeneration….