If this is a standard 3-way light switch (at any given time, the light can always be turned on or off from either location), the fix is easy.
1. Turn Off The Power.
2A. Remove one of the switches, turn it over and put it back in.
------- OR --------
2B. Remove one of the switches and swap the two "traveler" wires. These are the wires to go to the other switch. Since I can't possibly know what color they are or anything like that, the best reference I can give you is that they will be connected to similar looking screws on the switch (probably silver or brass colored).
The third screw on the switch (which you dont mess with) will be a different color, painted black or somehow marked as different than the other two screws. Do not confuse this with the ground screw (if you have one) which will be Green and have a bare or green wire connected to it. You wont mess with this one either.
3. Turn the power back on, Enjoy an orderly life.
Obviously, you chose option 2A. Don't have to mess with the wires or anything other than stuffing them back in the box.
This Will work. Guaranteed. If someone says it wont, I'd like to hear the explanation. Let me know how you make out.