Hello!
It sounds like the Bulk Administration Tool is definitely the tool you would need to use to change this amount.
The process depends on what version you're using.
In general you want to export the data for your phones / users, and then reimport it. Here is the BAT guide:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/bat/8_0_2/bat-802-cm.html
Respond back with your version and I can provide some more details.
-Jason