Download the launcher and put it on the hard drive you want to install to. You can select your install path/location before starting the download e.g. "D : \ The Elder Scrolls Online".

Yeah, very easy to move entire game to new disk.

What I did, first, was install my game to my larger drive due to immense installation, disk-space, requirements;

then later on, I wanted to see if I could change the "Install directory"
such that I would play off of a S.S.D. (solid state drive).

I copied the entire root folder off "The Elder Scrolls Online", and pasted it to said drive.

Then, i located
"..\The Elder Scrolls Online\Launcher\Bethesda.net_Launcher.exe "
double clicked that and according to "Task Manager" the data is being sought off of the desired S.S.D. drive.

I left out that the folder containing "The Elder Scrolls Online" root folder...
is on both drives within the folder "X:\Games\The Elder Scrolls Online"
; where x is the name of any disk in question.

Happy gaming.
I'll make sure to edit this post if the experiemnt implodes on me.

but if i installed a game to a disk E: (in my case, as C is for the system and it is full) can i be sure that the game uses a free space from disk E as well? There is no options to check it out.
as 3 days i can't login...