Software Deployment

I'm new to this packaging so please bear with me. I have created an unattended msi that installs Citrix Client 8.1 fine. I am now trying to modify it to uninstall 8.0 before the 8.1 installation goes ahead. I am using Wise Package Studio.

Things I have tried -

Wrote an embedded vbscript that used msiexec /x but this failed due to an installation msi already running (silly of me but worth a try)

Adding the previous 8.0 version to the Upgrades Under Installation Expert

Nesting an MSI using the Install MSI from destination to uninstall

When you install 8.1 by itself all goes well, however you must reboot once finished. This is OK. However with 8.0 already installed and trying the above methods 8.1 seems to install and then also asks for a reboot, but on logging back in, the installation tries to continue again and do more installation which then can't access the network share it was installed from.

To test things I wrote a two line vbscript that uninstalled 8.0 and then installed 8.1 as below
Shell.Run "MsiExec.exe /qn /x{2C42ED1E-6315-4E63-89E6-057EA114EBB8}"
Shell.Run "MsiExec.exe /i ica32cfg.msi"

This works fine and 8.1 installs as it does normally when 8.0 is not on the machine. Any help to uninstall 8.0 properly before installing 8.1 would be much appreciated.