After completing an upgrade of EXACT, You will be presented with a workstation upgrade monitor which will show the current update status of the current and historical workstations.
To clear this list of any old workstations:
Open File Explorer on the serve rcomputer and go to C:\Program Files (x86)\Software of Excellence\EXACT Server\EXACTResources
Open PushInstalls Folder
Delete any text document that has an old PC name and it will disappear from the list next time you perform an upgrade