Where are you having trouble? I assume you've got a MICS, DTI card, and PRI enabler.
After your hardware and keycode are installed, goto Maint, and disable the card. Goto Hardware, and change the card type to PRI. Make sure your settings reflect the CO's settings. (ESF, B8ZS, etc...)
Build your DID's, making sure your receive digits reflect what the CO is sending.
Build a route and destination code to dial out on the PRI.
I'm sure there's a FAQ on this.