Nortel Meridian 1 Manual page 204

83 To continue ugrading the RT to release 21, proceed with step 84. If you
are upgrading the RT to an option 61C X11 release 22, remove the
database disk and use the procedures in Upgrade system installation to
X11 release 22 (553-3001-258) to upgrade the system hardware and
convert the software to release 22.
84 Verify the system by using the test procedures described in Meridian 1
system installation procedures (553-3001-210) and X11 input/output
guide (553-3001-400). Clear any faults discovered during testing.
85 Follow the "Postconversion procedure" in Software conversion
procedures (553-2001-320).
The SL-1 X11 release 21 RT system is now operational. Install all covers to
complete the upgrade.
Upgrade system installation Upgrading to Meridian 1 system options
SL-1 RT system upgrades 5-19