Either they gave you too much sugar or your brew hadn't completely fermented out before you bottled.
Keep the bottles as cold as possible. The warmer they are, the better chance that the bottles will rupture.
If you're lucky enough, you can just open the bottles, let them sit for a while to degas, then recap them. However the odds are that they will just foam over when you open them. If so do the following (tedious) procedure:
- Lift the cap very lightly with a churchkey, just until you hear gas starting to escape. Don't take the cap off, the bottle will just foam over
- If you start getting foam, tighten down with your bottle capper
- repeat until you can lift the cap lightly without it foaming over.
At some point drink a test bottle. Use this to calibrate your degassing process, and to reduce the overall tedium