In the new Google Drive there is no “X” to clear out the search terms like you could with the old Google Drive. Rather than delete the search option character by character try using these keystrokes.
On a PC Control A selects all. This is Command A on a Mac. Use this keyboard shortcut to highlight all of the search terms in the Google Drive search box.
When the search terms are highlighted you can simply start typing the new search keywords, no need to hit the delete key.