Works only with dynamic HDDs!
1. Backup!
2. Remove old / unused Packages
3. Remove downloaded Packages: sudo apt-get clean, Remove only old downloaded Packages: sudo apt-get autoclean
4. "ZeroOut" unused Space: cat /dev/zero > zero.dat ; sync ; sleep 1 ; sync ; rm zero.dat
5. Under GUI: "sudo vmware-toolbox" and use shrink on "/"
6. Under VIClient: Defrag