A successful method for me is to heat up the label with a hair dryer if possible, to try and make the sticky stuff more pliable. Through trial, error and experience it will be possible to gently lift a corner of the label with a modelling knife blade. In doing this it will be obvious if this label is going to be removed with ease and with care and you can continue to use the blade to keep teasing the label away from the surface of the box.
If you have successfuly removed the label but there is still sticky stuff left on the box this is harder to remove without inflicting some damage or after effect to the box, depending on the type, age and quality of the card used for making the box.
When this has happened for me, I use an office eraser such as this one below.

For what it is, it is quite expensive but is the best out there for this type of work as it will also clean rust of axle-ends, scuffs of painted bodies and clean a lot of plated parts like chrome bumpers etc.
just gently rubb the sticky stuff with the rubber like you are trying to erase it and you may find it moving to a different area on the box which is fine as you can tease it to an adge where you can simply pick it off with a finger!
Sometimes the sticky stuff has embeddied a residue right into the surface to leave a darkened area showing where the label was. This is not going to be removed by any method and will always be visible so sometimes it is best to leave label in place!
Ghosthunter.