GL-MT300N-V2 - access to file sharing


I can access my usb key connected to my GL-MT300N-V2. I try to do what the tutorial says: Admin Panel -> APPLICATIONS ->
But i dont have file sharing: obly plugins(where i didnt find filesharing), dynamic DNS and GoodCloud.

Can you please help me?

Thank you in advance

On firmware 4.x the file sharing feature was removed due to performance problems.
Please follow How to install nas functions manually to get it back.

Thanks for your answer.
Seems that my router doesn't have 20mb free space. Is it normal?
My only solution is to downgrade the firmware right?

Downgrading or extroot if possible, yep.