Hi,
First of all, start with the official Cisco guide for this phone model, paying special attention to the section Configuring the Cisco Unified IP Phone 9971. During upgrade, you will need DHCP and TFTP servers which may be deployed on the same machine where Asterisk runs.
By the way, have you already set up any SIP softphone together with your Asterisk instance? If not - it should be the first step to perform since setting up a Cisco IP Phone is more complicated. For a Softphone, try X-Lite.