1) If not already running, start the Remote Registry service on the remote machine using PSTools
In an elevated command prompt, navigate to your PSTools directory and execute:
> psservice.exe \\computername start "Remote Registry" -accepteula
2) Next in the elevated command prompt, open the Registry Editor:
> regedit
3) Click File -> Connect Network Registry...
4) Type in the remote computer's computer name (also used in step 1) and click OK
5) Expand the newly added computer from the left pane to view the registry keys
6) Expand HKEY_USERS - the currently logged in user will be the longest key without "_Classes" at the end of the name
7) To confirm the username of the currently logged in user, navigate to HKLM\CurrentControlSet\Control\hivelist and looking at the matching SID in the string name. The user's username can be found in the value of that string.
8) Disconnect the remote registry under File -> Disconnect Network Registry when finished
SOURCES:
"Accessing 'HKEY_CURRENT_USER' on a remote machine" -
https://community.spiceworks.com/topic/138653-accessing-hkey_current_user-on-a-remote-machine
"Run commands remotely with psexec" -
http://heresjaken.com/run-commands-remotely-psexec/
"PSTools" (Suite Download) -
https://technet.microsoft.com/en-us/sysinternals/pstools.aspx
"PSService v.2.25" -
https://technet.microsoft.com/en-us/sysinternals/psservice
"Connect to the Registry" -
https://technet.microsoft.com/en-us/library/cc732388(v=ws.11).aspx