How should I destroy a Mob Spawner?
Solution 1:
To break one, use a pickaxe, preferably Iron level or higher. Note, once you destroy one, it will not drop as a block, so break these only if you'd like to get rid of them permanently.
While your opinion may differ, I find spawners to be excellent exp farms, and you can turn yours into a mob farm.
If you'd rather save your Mob Spawner, you need to block it off with light, similar to placing torches in a cave to ward off mob spawns. To de-activate a mob spawner, place torches around the spawner (at least an 8 block radius) to prevent mobs from spawning. Put them adjacent to the block itself.
Solution 2:
I always surround them in cobblestone, just in case I want to harvest later.
Pop torches all round to dissuade spawning, then build walls, ceiling and a floor.
When you want to harvest, build your grinder below and then knock out the floor and remove the torches.
And then run away :-)