Dealing with older long-term tenants on a new investment

[Troy B.]

I'm in the process of closing on a duplex property where both units have 80 yr old tenants that have been living there for 15+ yrs with very low rent. The ladies keep the apartments very clean and neat but the rent they have been paying are 50-60% lower then the current market. I would like them to stay but can't keep them at the current rent with a new mortgage to pay. They have no leases. Should I up their rent gradually once I own it or just tell them the new rent and let them decide to stay or leave?