i’ve known for a while that in windows server 2008 and above you could use diskpart to extend a volume (no 3rd party partition app required).
the method i’ve used before:
diskpart
select volume <volume #>
extend
exit

however, earlier in the week i witnessed ben using this:
diskpart
select volume <drive letter>
extend
exit

and i find that much quicker/easier to do than the above .