AMP’s SFTP implementation can be thought of as a “dumb”/“fake” SSH environment. All it allows are file operations, with no other command line actions available to the session.
You’d want to connect using Putty on port 22 using whichever information Hostinger has given you. Somewhere in their VPS management setup they should have a root password you can use (that wouldn’t be in the AMP panel, but on their actual website somewhere)