Hi,
Please check the following wiki page:
http://wiki.scn.sap.com/wiki/display/TechTSG/System+Upgrade+And+Update
You can find all information what you need to do before you start your upgrade process.
I write here few of the main points.
- Check your system for inactive objects.
Also for programs and dictionary objects.
If you find any inactive object you need to do a decision:
- Is that an own development?
Contact with the developer and check the status of thet object.
If neccessary activate or delete those. - Is that a SAP standard object?
Check the version of the object, if that is still relevant try to activate those objects.
- Check that yout live system is using the latest available compatible kernel.
If not please upgrade you kernel first.
But please checkthe linked wiki page, ther you can find all the informations about your question.