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I take some note about website that I have used for this difficult work:
Official Microsoft Prerequisite Checklist:
http://technet.microsoft.com/en-us/library/jj822981.aspx#BKMK_UpgradeSP1Checklist
Step by step Windows Noobs Tutorial (I have followed this one)
http://www.windows-noob.com/forums/index.php?/topic/7437-using-system-center-2012-configuration-manager-part-11-upgrading-the-hierarchy-to-service-pack-1/
At this website you can find a different procedure.
http://www.sccm.biz/2013/01/sccm-2012-upgrade-to-sp1.html
If you want to do a preliminar backup you can follow the following Microsoft Article:
http://technet.microsoft.com/en-us/library/gg712697.aspx
Consider that with SCCM SP1 now you can recover a secondary site without to reinstall it.