Ok, i removed the VSA-Cluster by using "cleanup.bat"as noted in Removing VSA Cluster from vCenter Server.
But when accessing the "VSA Manager" tab in vSphere Client it is showing the same message "Increasing VSA Storage Capacity". So, how to reset VSA Manager to initial clean state?
Recreating the Datacenter resolved the issue.
- create a new Datacenter
- move the hosts into new Datacenter
- delete old Datacenter
- rename new Datacenter to original name
- VSA Manager is now showing initial dialog