Ciao
If I understand the question correctly you need to free up the disk space in the datastore.
The thick format does not allow for the possibility of having only the space actually occupied on the VM by the OS and the data allocated to the datastore. You need to convert the disk (or all disks of the VM) to THIN format.
To do this you have to follow this KB (in the second part of the KB):
https://kb.vmware.com/s/article/2014832
Be aware that if you have many THIN disks you must monitor the size of the disks and the space occupied on the datastore. it is very easy to overcommit occupied space