Comment 9 for bug 1157497

There are various ways of applying patch depending on the OS your OpenERP server is running. Let me share a few,

Note: From the traceback provided in bug report, I'll assume that your audittrail.py(which contains fix) is located at path in your Ubuntu machine, /opt/OpenERP/server/openerp-6.1/openerp/addons/audittrail/audittrail.py

Now, you can use the patch command from terminal like this,
patch /opt/OpenERP/server/openerp-6.1/openerp/addons/audittrail/audittrail.py < audittrail_res_user6.1.patch

or, you can manually go to the file location and open the file in your desired editor and make the changes by yourself.

After successfully applying the patch, you need to restart the openerp service, below command should do it(assuming "openerp" as the OpenERPV6.1 service name),
sudo service openerp restart

Hope this helps.