1.) Extract the contents of Unofficial Skyrim Patch.7z, except for the FOMod folder (which is used by Nexus Mod Manager) into your SkyrimData folder. The default location is C:Program filesSteamSteamappscommonskyrimdata. There should be an ESP file, BSA file, and BSL file. The BSL file is not necessary unless you have need to use the official archive.exe tool to examine the BSA contents.
2.) Check Unofficial Skyrim Patch.esp in the Skyrim launcher if it isn't (it should already be after installation.)
3.) Using the arrow buttons, move Unofficial Skyrim Patch.esp so that it's the topmost .esp file (but under .esm files, if any.) This is so that it loads first and thus doesn't undo other mods' changes. This is very important if you use other mods. It is strongly recommended to use BOSS to manage the load order.
4.) Click Play and enjoy your much-improved Skyrim.

4. Uninstalling (Manual Version)

1.) Use the Unofficial Skyrim Patch.7z archive as a reference to what files you need to delete.

NOTE: On the off-chance that removal of the Unofficial Skyrim Patch causes your gamesaves which it was active in to fail loading, go to an untouched area (enter coc qasmoke into the console to get to a test cell, save your game then quit and remove the Unofficial Skyrim Patch, then cow tamriel 0,0 will return to the center of the gameworld.)