How do I get rid of old 10.x patches or superseded patches?

DO NOT USE SWREMOVE!  swremove will check the scripts for
the patch you ask it to remove, and happily remove whatever
file you tell it to, and replace it with an earlier version
of the patch from /var/adm/sw/patch/ (if one exists).

NOTE:  If you have already removed previous OS version
patches with swremove, you will either
1) need to restore from backup, or 2) reload the OS.

First download and install one of the following patches,
which contain the HP-UX patch tools:

o 10.x:  PHCO_20824  ('cleanup' only)
o 11.00: PHCO_27779  ('cleanup', 'check_patches', &
                   'show_patches')
o 11.11: PHCO_27780  ('cleanup', 'check_patches', &
                   'show_patches')

The patch tools come with 11.00, but you should still install
patch PHCO_24347 to fix several bugs that exist in it.

The 'cleanup' tool is used to commit patches while preserving
a set level of rollback, remove HP-UX 10.x patch information
from the IPD, and prune superseded patches from a depot.
The 'check_patches' utility checks for partially installed
(split) patches, incorrect patch_state, patch attribute
corruption, and objects within an archive library.  The
'show_patches' tool can display the set of active or
superseded patches on a system.

To remove old 10.x patches from /var/adm/sw/patch/, use the
command:

# cleanup -i

Committing a patch causes rollback files associated with
that patch to be deleted from /var/adm/sw/save/.

To commit all patches that have been superseded at least
twice, use the command:

# cleanup -c 2

On 11.x, to commit a patch that has not been superseded,
use the command:

# swmodify -x patch_commit=true 

In case you were wondering, 'cleanup -c 0' does not work.

WARNING: Once the above swmodify command has been executed,
        you CANNOT roll back (remove) the patch unless you
        remove the associated base software that the patch
        modified.  For this reason, I do not recommend
        doing it unless you desperately need to free up
        space under /var, and you have exhausted all
        other means of doing so.

Reference:
http://www.faqs.org/faqs/hp/hpux-faq/section-158.html