i want to know if i can replace my tention roller for timing belt with a different tensioner on my 02 vw jetta

I would stay with the same design. Unless the part has been revised by the factory and is different.

Are there two types of tensioners for your motor? What's wrong with the one you have now?

OEM roller should be about $25 at most auto parts outlets. If your current one won't release tension, it's a good idea to swap for new. The newer style rollers have two holes to use a special spanner to tighten...older ones can use a crescent wrench but are thicker and may not fit cleanly.