The "lease" you are referring to is the DHCP address lease, and not a "WiFi lease".
Think about it this way: In order to communicate on the network, your computer needs an address (sort of like a "phone number"). When your computer first connects to a network, it asks if anyone can lend it an address to use and the router responds with "here, use this information." Boom. You're connected.
The lease AUTOMATICALLY renews ITSELF when it reaches the midway point of its duration (if it's leased for two hours, your device will attempt to renew it at one hour). You can initiate the renewal process at any point without causing any harm. The renewal is a way for your device to ask the router if it's ok to continue to use the address for a bit longer than originally planned.