Bicycle Tutor

I can't get the cable out of the old brake levers. Any tips? I changing to a straight handlebar and need to change levers.

What type of handlebar/brake levers do you have now?

Before you do this part exchange you should get a cable crimp,just in case.
If you have V Brakes (the kind that are affixed to the frame via a brake arm on each side and joined together by a cable that runs though one first then the other) you will want to squeeze the brake arms together at a 90 degree angle and release the cable from the side with the guide then loosen the cable with the appropriate allen wrench (5ml).
If you have a cantilever brakes(the kind that has the cable running through a circular metal piece to one arm and another cable coming from that circular piece going to the other) you simply pull the two arms together and slide the cable out of the side its not bolted down in,then unbolt it from the other.The previous step will release all the cable tension.After you do that all you need to is line up the slit on your barrel adjuster (thats the cone shaped bolt on the end of your brake lever),with the slit on your lockwasher,
with the slit on your actual brake lever handle:now pull on your brake(which should have no tension on it now)and twist that little nob on the end of it till it slides out of the lever itself.
Your brake cable should be free now and as far as saving the lever mechanism the only practical advise I have is cutting the grips,because if you try to bend the band that goes around the handlebars out wide enough to remove it might never go back on the way it should. Also now is good time to check your brake cable for any kinks and oil etc.I also recommend waiting to put your brakes back together till you get your handlebars in place. One more thing to after you put your brakes back together is that your cable crimps haven't slid off... these are sold by the bagful and are inexpensive but keep your cable from fraying so its a good idea to make sure you have them in place.
Hope this helps,
BIKEGUY
P.S. my source:I assemble bikes professionally