On VCSA, the database is stored on a separate disk. It could happen that this disk runs out of room, causing Vcenter to no longer function properly. One way to resolve this is by running database clean up as mentioned in KB 2110031. However, if this is not possible, or you don't want to clear out the data, you can also resize the disk.
For this to work, you'll need root access and access to the bash-shell, either on the console or through SSH.
Before resizing, identify the physical disk to be resized. For VCSA 6.5 and 6.7, this should normally be Disk 8 (device node in linux = /dev/sdh), but your setup may vary, so it's best to double-check this.
Handling snapshots (creating, deleting, restoring) is rather intuitive when you already have some experience with PowerCLI. As a reference, here are some one-liners. As always with Powershell, there's more than one way to achieve a goal... The examples used here assume a VM named "SRV01". Adjust as needed.
Create a snapshot:
Get-VM SRV01 | New-Snapshot -Name "My snapshot"
Remove all snapshots (disabling confirmation request in the process):