If you need to upgrade the license you will need to buy it first. You might be able to get it by getting in touch with your local Cisco reseller.
After getting the license you will need to enter it on the pix by using the command:
To obtain a Activation Key or License, all customers must obtain a Cisco.com user ID.
Once you have obtained your Cisco.com user ID, please log on to http://www.cisco.com/go/license to obtain Activation Key or License.
Please note: The Technical Assistance Center (TAC) will not be able to provide the FREE Activation Key or License to customers, and will re-direct all customers to the process described above.
Thank you in advance for your patience and acceptance of this process
In addition ,
you need purchase FO to UR platform license upgrade PART# PIX-525-SW-FO-UR= , see table 11 & 13.. and as previous posters indicated you need contact cisco for this or ciosc partner.. also look into mem requirements for UR.
Memory requirements for UR