Rename Z:

Go to This PC

Option #1: use the WINDOWS+E shortcut... 

Option #2: click on the Documents button on the taskbar, then click on Computer on the left navigation list.

Rename Z:

Right-click on the drive with your student number and "Rename". 

When everything is highlighted, you can replace it by just by typing; you don't have to delete it first. 

Once you've typed in your first name and hit Enter, you'll see Z: now.