Rent increase to inherited tenants

[Bobby Balentine]

Good evening all.  

When purchasing a property that has tenants and you take possession on the 6th of the month, at what point do you notify the tenants of the increase in rent?  Tenants are currently on a month to month lease.  Should you offer them a choice of yearly lease, 6 months lease, or month to month, and if so, would you charge a different monthly total rent for each choice(ie yearly monthly rent $600, 6 months monthly rent $610, or month to month monthly rent $625?)

Thanks in advance for you thoughts!