It is absolutely essential that you ONLY replace failed units with exact replacements. Any subsitutions will void all warranties.
To replace a Unified Burst Disk Assembly, simply unscrew the failed unit, and discard it. They are NOT serviceable.
Screw in the new replacement unit and torque with torque wrench to 55 inch-pounds. Do not over-torque.
These are rated to 3k PSI.