Go to your Program Files and find the folder for Zenimax Online (for 64-bit users, this will be in the Program Files (x86) directory). If it starts to install, hit pause and then close the launcher. Under the megaserver drop down menu, click on the one you wish to switch to. Load the game launcher and click on the cog icon in the upper right hand corner. I have gone step-by-step through the process to document what to do to get the second megaserver running on your PC. Good news: You do not have to download again to switch megaservers.