I'm assuming you want your skin to use the beatmaps skin
Just remember that if you do choose to use it, it won't have any of the other elements (e.g. Menu, Options), so it could look out of place.
So copy everything except for BG.png, SB (Folder), .osu / .osb files, .mp3 files and the .wav file.
After that, just drag it into the folder of the skin you're currently using or the one you want to change (Creating a new folder and placing them there should be fine as well).
After that, head into Options > Skin and select it.