In San Francisco, what are options for removing tenants w/o evicting them?

I’m thinking of buying a two-unit SF house in which one of the units is occupied by a renter. What are the options for removing tenants or motivating them to move without evicting them? If I offer to buy them out and we have a binding contract, can they then refuse to move and force me to evict them? Where can I learn more? Thanks in advance.