I currently have a bright red box die on my undercut. I would like to transistion to the electric blue. Will this remove the color enough to do that?

There is no way to tell in advance - but it will do a decent job for initial lift. Typically, box dye uses an oxidative permanent color that swells the molecules and jams into your hair shaft. Lightener will open this up and start removing the color - but each color line and your hair will react differently. You will want to lift your hair past the orange into yellow - and remember, blue + yellow = green. So if you are going for a pale blue, lift to very pale. If you are going for dark blue, regular yellow should be okay. Be sure to check your hair to make sure it can handle the lift several times while you process. Good luck!!