You may find that your cube is very stiff to turn, in which case you will need to open it up and grease it a bit with a petroleum jelly, like Vaseline.
To open the cubes turn the top slice through 45o and insert a screwdriver under one of the edges and apply a gentle pressure to it until the edge piece pops out. The two loose corners will then easily come out. Now you will be able to reach to the centre of the mechanism of the cube and apply some Vaseline there.
If you find that the stickers have worn out, don’t worry a bit. New stickers can be now bought from many stationeries. You can even have a great fun by making your own stickers and giving your cube truly individual touch!