Go to Settings>iCloud, tap Delete Account, then sign back in with his iCloud ID. If you need to migrate your data to his account and merge it with his, choose Keep on My iPad when prompted, then choose Merge after signing into the new account to merge your data with his.
A word of caution - when you share an iCloud account, any data you both sync with the shared account is merged, and the merged data appears on all devices. You will, for example, end up with each other's contacts on your devices if you both sync contacts with the same account. Also, any action you take with this data on one device is synced to all other devices sharing the account. If you, for example, deleted your husband's contacts from your iPad, they would also be deleted from his devices (and vice versa) and they would be lost.
You will also be sharing the same 5 GB of free iCloud space for your data and backups.
If you don't want to share your data like this, you should continue to maintain separate iCloud accounts.