This is the plugin version of the older Median XL, so you don't have to worry about replacing files or any of that hassle, so you easily switch between mods. Median XL Ultimative is already compatible as a D2SE plugin.
This are the instructions how to install or remove D2SE Modplugins. Modplugins are mods that are modified for the player to be easy-playable using D2SE. Modplugins do not change your basic D2 installation, so you can play on official bnet without worries (starting the usual game.exe). Another important thing to know is, that with D2SE every modplugin has its own SAVE folder INSIDE the plugins folder for your savegames. Logs and Screenshots are saved there too. Modplugins do NOT use the usual SAVE folder inside your D2 folder. Installing the modplugins is easy - you just have to to extract the files into mods-folder of your D2-installation (which was created by D2SE), thats it. After extracting the modplugins there will be an own folder for each mod inside of the mods-folder.
The best start is to control if the MODS folder inside your D2 folder really exists. If not please install D2SE Modmanager. HERE.
Full List of D2SE Plugins: Snej.d2maniacs.org