In Windows store juliaup is named Julia 
It comes with some version of Julia that you will need to update via juliaup in the powershell.
The Julia app name is assigned in your PC (you should uninstall previous Julia instances not installed with the Julia(up) app). When you launch the Julia app from Windows Start menu, you get a REPL using the default Julia version you defined in juliaup. Or just get the REPL by typing julia in the powershell.
NB: for a nice Windows experience, I would recommend using Jeeves.