House with in laws suits

[Anastasiia Greca]

Hello!
We are in a tricky situation and will appreciate any advise!

We were originally planning to buy duplex, so we could rent one unit and live in another. But ended up buying a house with a big upstairs "in laws suite". How do we rent it out legally? do we need to turn it into multi house first? do we register it as rental as it is? what is the legal process before we start posting adds and start looking for tenants.
I understand we should had think this through prior to buying, but numbers looked good and we went for it.