You can create a custom market and trade your SnapSwap's crypto assets into XRP or another currency.
Unfortunately, the SnapSwap/btc2ripple gateway seems no longer operational, so the value of their crypto assets has been very low on the market.
If you are unable to trade the SnapSwap crypto assets, you can send them to the issuing address (the trust line address), to free the 2 XRP reserve for the SnapSwap trust line.
Once the balance in the trust line is 0, you can disable the trust line, to make 2 XRP available.
Please note that sending the crypto asset to the issuing address means you are giving up the funds.
Withdrawing the SnapSwap crypto assets to native addresses (e.g. SnapSwap BTC to Bitcoin address) or exchanging them through the GateHub client is not possible.
SnapSwap / btc2ripple & defunct gateways