Cannot restore my admin functions

Hello, Everyone!

I used a freelancer to do some stuff on my website. I created him an admin account. After the job was done i saw clues that i’m not the “ADMIN”. When there is a wordpress update it shows me to “notify the administrator”, the plugins update notifications are not shown. I cannot delete Plugins or Themes etc.

There is some “admin” user which i cannot delete from the frontend (Dashboard) and from the backend (phpMyAdmin). It appears after 30 seconds.

Help! What should i do? How can i restore my superior administrative capabilities and delete the account once and for all.

Thank you!