With Minecraft now using uuid method for authenticating users instead of the old classic usernames, some gaming conventions have changed.
To give yourself your anyone else OPs, we now recommend using the console.
Say if your user name was ULTRAMOO
1) Start your server
2) Type: op ULTRAMOO
(Note, put your user name instead)
3) You now have Op! Now you can add others from with the same.
If you want to revoke ops, do the same as above except for step 2 it would be: deop USERNAME