Raising rent with a new contract

[Brandon G.]

We're about to close on our first property, a duplex.  One side is recently vacant, the other is rented.  The current rent is 600 and we're going to raise the rent on the unrented side to 700.  I'd like to raise the rent on the currently rented side in about 6 months.  A new lease agreement will be signed by the current tenant.  My question is, if the tenant signs a year lease at $600 month, what do I need to do to be able to raise that rent to $700 in a few months?  Can I simply state this in the lease agreement when he signs in?

Thanks,