You can use method like
upgrade using DBUA
Start from here :Contents
There are no. of steps you have to follow during this.. do some Google or follow the Oracle Doc. and Try to do on on your test Db first..
If you get any Error you can post here with the detail log
Hope this help
PSU ==> Patch set upgrade/update (start from version 11g) release Quarterly
CPU ==> critical patch update/upgrade (below 11g) release Quarterly
Interim patch ==> Interim patches are bug fixes available for specific bugs.
SPU ==> Security patches update/upgrade
And rest i think u should read from here :Patches and Updates
Master Note For Oracle Database Upgrades and Migrations [ID 1152016.1]
Different Upgrade Methods For Upgrading Your Database [ID 419550.1]
For all upgrade process Please check my blog
In this pdf you can see patch of to upgrade db from x to n wiht many senerios wiht all related metalinks notes which is created by *Oracle worker Mike Dietrich*