Rehabbing a tenant inhabited duplex

[Bryan Berrios]

I'm looking at a duplex that has been on the market for about half a year. I'm assuming it's been on so long because the pictures show it is highly outdated. Despite that, the listing says both sides are currently being rented out. My question is, how do you plan a rehab for a property that has tenants in it? An eviction? Do leases lose authority over new owners? If I were to buy this property, I would want to rehab the whole house and rent it for more than it's getting now. Any help is appreciated.