Uninstall Store Commerce app using Power shell

 1. Search for the full package name of the current MPOS using command 

Get-AppxPackage -AllUsers

or 

Get-AppxPackage *pos* --AllUser

then find the package of the Microsoft.Retails

2. Uninstall the package using below command

Remove-AppxPackage -AllUsers <Package name in step 1>

3. Go to Control Panel to find the Commerce app and uninstall it.