open search icon in taskbar then type roblox and Press Left Button in Mouse then choose Uninstall .
then wait 1 minute to roblox uninstalling .
2- Remove Roblox Folder
press search icon in taskbar then type control panel then in option View by in Top Right choose Larg icons then choose File Explorer Options then view tab then choose show hidden files, folders, drives option then press apply and ok .
go to C Drive then Users Folder then choose your user name then choose AppData Folder then Local Folder and Scroll down to Roblox Folder and remove it .
3 - Reinstall Roblox
in this article How to Download and Install Roblox on Laptop or Pc you can download and install roblox by two ways .