Different types and versions of Autodesk products have different policy of installing Service Packs (or "Product Updates").
E.g. starting with Inventor 2012, every higher Update (SP) also contains all lower (older) Updates and so it is not neccessary to install the whole history of updates - you can directly apply e.g. "Update 2" (Service Pack 2) to the original version of Inventor (sometimes called "SP0", "RTM" or "FCS").
If you apply the updates incrementally, you can also uninstall them incrementally. So by uninstalling SP2 you will get Inventor with the SP1 installed, including its possible hotfixes installed before SP2.
To distinguish whether a particular Service Pack contains also the older SP versions, or whether it requires to install them, you can use the description of the Service Pack on our www.cadstudio.cz/download page. The text "incl.SP1" means "already contains also SP1", on the other hand the text "reqs.SP1" means "requires a previous installation of SP1".