Hi,
In the technical upgrade, you have to taken care of testing activities, like pre support pack and post support pack, Execute all your master data, transnational data, table entries and report and record the results, after support pack upgrade from the basis, Run all the transactions, which were executed in Pre support pack and see is there any differences and record the results.
Also Basis will provide you the bundle of OSS notes, which contains all the changes.
In one sentence I can say that, you have to test all functionalities.
Regards,
Ravi