To uninstall patch kits, you can use the PRODUCT UNDO PATCH
command. However, this command works only if you have installed
the kits with the /SAVE_RECOVERY_DATA qualifier. Also, the saved
recovery data must be available on the system, which is possible
only if, after installing the patch kits, you did not perform another
operation that deleted the patch recovery data. Operations that
automatically destroy recovery data sets are the following:
After using the PRODUCT SHOW RECOVERY_DATA command to verify
that patch recovery data is available, you can perform the uninstall
operation using the PRODUCT UNDO PATCH command. This command allows
for some flexibility:
By default,
if you do not use any qualifiers, only the latest installed patch
kit or kits are removed.
If you want to uninstall
all patch kits to the extent that recovery data allows, use the
/ALL qualifier.
To limit the number of patch
kits to be uninstalled, specify the /NEWEST=n qualifier, where n
is the number of the newest recovery sets.
To uninstall patch kits that
have been installed after a certain date, use the /SINCE=date qualifier.
HP OpenVMS System Manager's Manual, Volume 1:... 
Installing, Upgrading, and Updating Software
