Download the skin to your phone.
Open Root Explorer
> Go into SD Card > Downloads > Find the downloaded skin
> Select Menu > Move....
Back out of Downloads & SD Card...
Open.. System > Apps
> Select Menu > Paste.
On the top right of Root Explorers screen
> Press Mount/RW
> Click on the Skins file and choose Install... the downloaded skins .apk file will install.
On the top right of the screen
> Press Mount/RO and exit the app.
Go to the Sense Skin picker under Personalize on your phone... your new skin should now be listed as an option.