Buying Duplex with Existing Tentants: What to do?

[Tou Vang]

I try looking this question up but nothing shows up. Maybe the way I type it into the search engine.

I'm planning to buy a duplex and it tenants occupied.

How do I work this out with the owner or what needs to be done here? What do I do with the existing tenants? Re-sign contract, re-screen, etc.