"Move Selection" menu option describes Hotkeys for Selection Tools line:

Increase Up. Hotkey is SHIFT + Up Arrow

Increase Down. Hotkey is SHIFT + Down Arrow

Increase Left. Hotkey is SHIFT + Left Arrow

Increase Right. Hotkey is SHIFT + Right Arrow

Decrease Up. Hotkey is Alt + Up Arrow

Decrease Down. Hotkey is Alt + Down Arrow

Decrease Left. Hotkey is Alt + Left Arrow

Decrease Right. Hotkey is Alt + Right Arrow