df -h show that the size of / partition is only 3.9G and using 3.6G but when I ran gparted on it I get that is is 100G. How do i expand it to use more of the disk space.
Not sure if this is OH related but you can try using the openhabian-config tool, select number 10 Apply Improvements then number 13. If that does not do what you expect then you may want to do a google search for partition management.
Many times newer Linux systems have many partitions. openHAB nay not be installed on the / (root) partition.
As it’s a vm, it’s depending on the underlying technique.