Hi Massimo,
There are a few methods to install an SDK into the IDE.
1.) Drag/drop an SDK into the Installed SDKs view. This will create a copy of the SDK package at a default location c:\users\<>\mcuxpresso\SDKPackages. If you right-click in the installed SDKs view, and select Open Default Location, this folder will be opened in windows explorer.
2.) Store SDK(s) in a folder on your file system. Point the IDE to the folder containing the SDKs by adding the path to the SDK root list in the IDE Windows>Preferences>MCUXpesso IDE>SDK options. SDKs can be added/removed directly from the folder. If you select an SDK package in the installed SDKs view, right-click, and select Open Location, the folder containing the selected SDK will be opened. To use option 2, it is not necessary to delete the <>\mcuxpresso\SDKPackages folder.