Increase lockin period

Good Evening All,

We have entered into a lease deed for a property of a fully furnished Office Space for 6 years where in lockin period was fixed to 3 years. Now that the lockin period is going to be completed by March 2018, we would like to further extend the lockin period for the next three years. Kindly guide me through the process for extension of lockin period? Both the parties are interested in the extension of the same.

Please advice.
Regards

Aneesha