Missouri purchase of rented multifamily - lease changes?

[Lynne Hart]

Helping a client buy an occupied multifamily and he may want to change some things about leases after close.  I've never actually done this, always just rode the leases out and then renewed on my own contract, primarily I assumed I had to.  So, questions:

 - Must the current leases be honored in exact terms? (not wanting to kick anyone out, but may want to adjust policies)

- If someone is in a unit on a lease that expired a long time ago, I assume we can put them on a new lease after close assuming they don't elect to move out.  

- Even if we didn't change policies or terms, can we update the existing leases to the buyers preferred contract if the basic tenant cost and amenities, etc don't change?

General boundaries and guidelines with leases after close would be appreciated.  I can't seem to find information in the missouri statutes, must not be using the right words!!