To view the local admin users of the PC you are currently using:
net localgroup administrators
After downloading and saving
PSTools to a folder, which include psexec.exe, and making it available globally through System Variables -> Path, you can run the "net locagroup" command on remote PCs, given that you already have local admin rights to those PCs.
To view the local admin users of another PC remotely, try
psexec \\<ip_address> net localgroup administrators
To add a user to the local admin group remotely:
psexec \\<ip_address> net localgroup administratos "<domain_name>\<username>" /add
To remove a user from the local admin group remotely:
psexec \\<ip_address> net localgroup administratos "<domain_name>\<username>" /delete