I rented some rims from rentawheel and have been making payments for about 3 months but I have lost my job and haven't been able to keep up with the payments, they informed me that if I don't come up with the money they can charge me with grand theft.

True. If you don't pay you give them back or be charged with theft. They are rented which is much different than if you were buying them.

Yes, you will have to either pay them or return them. *** You also need to read your contract as to the provisions you signed to when you got them.