To uninstall the patches from local client and tools follow belwo steps:

1. Set home directory set ORACLE_HOME=C:\Siebel\8.1\Client_2
2. List applied patches: opatch lsinventory
3. Uninstall: opatch rollback -id <patch number>

Actual step execution in command line:
1. Start run -> enter CMD click ok and then
cd C:\Siebel\8.1\Client_2\OPatch
C:\Siebel\8.1\Client_2\OPatch>set ORACLE_HOME=C:\Siebel\8.1\Client_2 C:\Siebel\8.1\Client_2\OPatch>opatch lsinventory Invoking OPatch 11.1.0.6.0
Oracle Interim Patch Installer version 11.1.0.6.0
Copyright (c) 2007, Oracle Corporation.  All rights reserved.

Oracle Home       : c:\siebel\8.1\client_2
Central Inventory : C:\Program Files\Oracle\Inventory
   from           : n/a
OPatch version    : 11.1.0.6.0
OUI version       : 11.1.0.6.0
OUI location      : c:\siebel\8.1\client_2\oui
Log file location : c:\siebel\8.1\client_2\cfgtoollogs\opatch\opatch2011-07-05_14-50-31PM.log
Lsinventory Output file location : c:\siebel\8.1\client_2\cfgtoollogs\opatch\lsinv\lsinventory2011-07-05_14-50-31PM.txt
--------------------------------------------------------------------------------
Installed Top-level Products (4):
Siebel Client enu                                                     8.1.1.0.0
Siebel Web Client                                                     8.1.1.0.0
Siebel Web Client PatchSet                                            8.1.1.2.0
Siebel Web Client PatchSet                                            8.1.1.2.0
There are 4 products installed in this Oracle Home.

Interim patches (1) :
Patch  8112212150221: applied on Fri Jun 24 17:00:40 EDT 2011
   Created on 12 Mar 2010, 21:07:22 hrs
   Bugs fixed:
     8112212150221
 
--------------------------------------------------------------------------------
OPatch succeeded.
C:\Siebel\8.1\Client_2\OPatch>opatch rollback -id 8112212150221 Invoking OPatch 11.1.0.6.0
Oracle Interim Patch Installer version 11.1.0.6.0
Copyright (c) 2007, Oracle Corporation.  All rights reserved.

Oracle Home       : c:\siebel\8.1\client_2
Central Inventory : C:\Program Files\Oracle\Inventory
   from           : n/a
OPatch version    : 11.1.0.6.0
OUI version       : 11.1.0.6.0
OUI location      : c:\siebel\8.1\client_2\oui
Log file location : c:\siebel\8.1\client_2\cfgtoollogs\opatch\opatch2011-07-05_14-56-11PM.log
RollbackSession rolling back interim patch '8112212150221' from OH 'c:\siebel\8.1\client_2'
Running prerequisite checks...
OPatch detected non-cluster Oracle Home from the inventory and will patch the local system only.
Backing up files affected by the patch '8112212150221' for restore. This might take a while...
Patching component oracle.siebel.client, 8.1.1.2.0...
Copying file to "c:\siebel\8.1\client_2\bin\sscfbas.dll"
Copying file to "c:\siebel\8.1\client_2\bin\sscfjs.dll"
Copying file to "c:\siebel\8.1\client_2\bin\sscfomlg.dll"
Copying file to "c:\siebel\8.1\client_2\bin\sscftclg.dll"
RollbackSession removing interim patch '8112212150221' from inventory
Execution of 'cmd /C "C:\Siebel\8.1\Client_2\.patch_storage\8112212150221_Mar_12_2010_21_07_22\original_patch\custom\scripts\post.bat" -roll
back 8112212150221 ':
Rollback of current QF is complete....
Return Code = 0
OPatch succeeded.