How to REHAB with tenants in place?

[Lloyd Stein]

I'm a newbie and the part I get hung up on is if, for instance, you find a 4plex with 4 long term tenants in place, how do you pull off the REHAB if they are in the apartments? I know this sounds like a minor thing to experienced investors, but I keep getting stuck when I try to imagine how I work around tenants to get all the apartments fixed up so I can raise the rents, the appraisal value and then refinance. 

Do you do the work while they are there?

Wait till a lease is up move that person out, fix that one, then repeat for each one?

I always imagined it's less money and hassle to pull off the whole rehab at once, but not sure how people are doing that.

I'm sure there is more than one way to do this, but I'd love to hear from some of folks who have pulled this off successfully.

Thanks,
Lloyd