Inherited tenants and rental increases/property updates

[Jennifer A.]

We are about to close on a duplex with rents which are under market.  Current tenants pay $750.  If we did nothing to the property we could rent it for $900.  If I did a bit of updating, I could rent the units for at least $950 per month (possibly $1,000+).  I'm sitting here debating between terminating one side (the side that is month to month) and updating it versus keeping the tenant and only collecting the $900.  I would need to update the bathrooms (they need it badly) and the carpeting.  Possibly appliances too.  I think it would cost me approximately $6,000 to do these updates.  What would you do?  The other side has a written lease that I will be honoring.