Hi Franko.  Sounds like you have a good thing going there and it could be even better if you could take advantage of the low interest rates while they're out there and still available.  Based on your post, you've got a little bit of equity there, which is a major plus right now as many people are upside-down in there mortgages these days.  You state it's rental so with a lower rate and lower payment it will give you a pretty fair increase in rental income potential, which is always a good thing.  If I were you, I would go ahead and discuss this option with your lender, and if they can't offer you the terms you are comfortable with, shop around and check out some other banks.  Fore sure at least one of them will be more than happy to have your business.

Best of luck to you.