Need help on extending tenants lease
 

Our tenants one year lease is soon coming to an end. They would like to extend it an additional six months, which is agreeable to us, since we need more time before we can make our move. Can we just add an addendum to the existing lease, where both parties can sign it? With the exception of the extended dates, we would like to keep all the terms the same. Any help would be appreciated.

Not a lawyer I think you addressed all your concerns.I don't see an issue

You need to do nothing. Extending the lease without a new Agreement turns the expired Agreement into a month to month term. Just make sure that you advise the Tenants IN WRITING at least 30 days before you terminate their occupancy.
Of course you could write up an Addendum but it's unnecessary especially since both you and your Tenants are "on the same page".

BAD Advice to do Nothing
 

Your original idea is the correct approach. Depending on how your lease is constructed, you either change the title page, which has beginning and end dates, or write a simple addendum that indicates the lease is extended at the new or same rental rate with the new termination date. If you do not formally extend the lease, it actually gives the tenants more control of their occupancy. Take the ten minutes to formally extend, especially if your tenants are in agreement.