Fully Occupied--When to raise rent?

[Andy S.]

I have a 15 unit apartment complex that I purchased at the beginning of the year. Most units are paying $550-575. I turned over 4 units so far and raised rents  to $700. The other 11 units are still  paying low rent (that's why I'm fully occupied). I have made many changes to the exterior (new roof, paint and landscape). I've been waiting for tenants to move out so I can turn over the units and raise rent, but no one moved out for the last 2 months. My questions are:

-When should I raise rent  (hopefully get people moving or at least compensate for the improvments)?

-By how much would you start to move rents by?

I'm thinking of raising the older tenants (11 units) $50 soon.

What do you guys think?

Thanks,