editing on “enter new filename”

Is there way to quickly remove the full title.
The only way I know how to remove letters is start at the last letter. Because that’s where the cursor is. Then press the arrow key on mykeyboard to remove one letter at a time.
Okay i see if i bring up “enter new filename” at the bottom there are two arrows to move the cursor left or right. But that is quite slow. Is there a quicker way, for instance to reach the first letter.
I guess I’m thinking of keyboard shortcuts.