The following high-level procedure will help you host all your VM workload on VMFS 6 volumes:

1. Make an inventory of all your datastores and their current utilization.
2. Now, depending on the amount of free space available in the storage array, you can choose to create LUNs of the same size as the existing datastores or create a set of larger LUNs to temporarily migrate the VMs onto them.
3. Once the datastores have been created, use storage vMotion to migrate the VM data on the datastores.
4. If you have created larger temporary LUNs, then select one or more datastores in batches, migrate VM data off of them, delete the empty VMFS 5 volumes, create a new VMFS 6 volume on their LUNs and migrate the VMs back to them.