Can I renew my domain name with you only and let the hosting account expire?
If the domain name is free with your account and you only want to keep it and cancel the account, then you could do that from your User Area -> Billing tab -> Cancel Services. Then click Cancel next to the entry for your hosting account and process its cancellation. On Step 3 you will be given a choice to keep the domain name or not. If you choose to keep the domain name, it will be kept active but it will no longer be renewed for free.
If your domain name is not free with the account, then if you let the hosting account expire, the domain name will not be affected by the cancellation as it is listed as a separate renewal in our system.