If you have someone assume the payments or give it back to the dealer you are technically selling it.
There are a few options. Get more money through a part time job; take it off the road thereby stopping costly insurance costs, which might help detract from your money payments, and you will still have the bike; arrange someone to take on the payments, or discuss with the dealer.
Keep in mind if you go to the dealer, you will have less of a negotiation possible.