When I try to edit items from the fron-end, I get this notice:
The item: testname is currently being edited by another administrator

and I can't edit it.

I'm the only person logged in the front-end.
How to fix it?

Thanks for your help!

Hi Elle,

Perhaps you are using 2 different accounts to login to backend and frontend, if this is the case and you edited the item from the backend without closing the editing form either by saving or cancelling the edit, you will find this message.

To fix it, login to the backend, find the item, click to open the edit form and close, then you will be able to edit from the backend.