Probably the most user-friendly way would be to use gparted (https://gparted.org) - I'd grab the live CD/ISO and set that as your boot drive for the VM running unRAID. It should see your existing vmdk and allow you to resize it. From memory (and this is going back quite a few years now so I don't know for sure!) the .vmdk file itself was already 1Gb, so you should be able to extend the partition to fill that.
If the .vmdk file itself also needs extending, you can do that from the command line in VMware, using the vmkfstools command. You can see more detail here. You would first extend the .vmdk file to a certain size, and then run gparted to expand the partition to fill the newly-created disk.
https://pubs.vmware.com/vsphere-50/index.jsp?topic=%2Fcom.vmware.vsphere.storage.doc_50%2FGUID-97FED1EC-35A5-4EF2-80BA-7131F8455702.html
There's quite a few other ways to approach this too, but that should specifically address what you need. Lastly, back up the .vmdk first in case something goes wrong!