How to renovate an apartment complex with tenants inside?

[Patrick Philip]

I've been looking at a 12-unit apartment complex. 9 units occupied, 3 vacant. There are many renovations I would do to the inside of each unit. Floors, painting, drywall, replacing fixtures, etc.

How can I do this while they are still under lease?

Or is my only option.... to renovate them while they're vacant and just tell the people the lease in unable to be renewed as they become available?