How to document transition of a tenant to new landlord (me)?

[Steve S.]

I recently acquired a property that has a tenant in a long term lease that they just started.  I couldn't find any obvious answers to this after some quick Binging so would like the BP perspective.  I've emailed them and told them who i am and where to make payments, how to submit maintenance requests, etc. 

What do i need to draw up and have them sign to denote I am now the Landlord and property manager?  In the state of Texas we have to honor their previous agreement so that won't be an issue, but some things will obviously change (including the named Landlord and where to submit rent payments and maintenance requests).