Instructions
Press "M" on your map once you enter Alterac Valley. Look for four towers at the bottom of the map. The first tower is called Iceblood Tower, the second Tower Point and third and fourth are named the East Frostwolf Tower and the West Frostwolf Tower, respectively.
Enter the tower by running through an entrance at the bottom. You'll run up a winding path to the top. Kill the guards at the top. You should be able to kill them by yourself. Run around the top of the tower until you see a room with a flag. Enter the room.
Right-click the flag. The flag will change from horde to alliance. Prevent the horde from clicking the flag for four minutes and the tower will blow up, awarding you honor points.