How do you deal with tenants paying very low rent?

[Joan Pla]

Hi all, 

I came across a very appealing 6-unit building in a great neighborhood and while looking at the current tenants' rent info, I noticed all units are paying incredibly low rent. The building is C-class but my idea would be to upgrade it to B or A. Now, the question I got is about these tenants, this may be a very basic question but how do you upgrade the rent to current market value? Do you need to kick people out at the end of their lease? What are the options?

I'd appreciate any help

Thank you!