How do I cancel my BTC transaction (Unconfirmed for 5 hours)?
There's not really anything you can do, other than wait. If the transaction isn't confirmed within ~72 hours of sending, it should be dropped from the mempool ie. returned to sender.

The reason your transactions isn't getting confirmed as fast as you're used to, is because the network is a little congested at the moment. It can only handle around 6mb per hour, and currently there's a backlog of around 35mb.