Long spurs can be troublesome in several ways such as by causing injuries to a hens back when mating and also general injuries when the spurs are being used as a weapon in fights between roosters (or worse still, attacking people) or simply getting so long that walking and perching is becoming difficult. There are several reasons you might want to trim or remove spurs and quite a few ways to do it.
One simple method is to trim or file the spurs down so that the point is blunter (like clipping a dogs nails). Removing the spurs altogether may be a possibility and may be something your vet would do if you were not comfortable with it. A few keeping chickens newsletter subscribers have mentioned successfully using the hot potato method which subscriber Carol Ehlinger mentioned in the September 2010 Newsletter :
"My older rooster is over 2 and he is getting large spurs. I read to trim them at the base or leave just ¼" so he doesn't bleed to death. I also read to use a very hot potato and leave them on for a few minutes and then twist the spurs off. The heat cauterizes the blood vessels. I followed the directions of using a hot potato. It works! I heated 2 small potatoes and went in after dark and held the rooster. He was very calm and docile. I held the potatoes on for a minute or two and twisted the spurs off. He hasn't seemed to be bothered by it at all."
This next method which was first shared in the October v1 2013 newsletter by Sandra Megyesi seems quite extreme (after all it does involve a pair of pliers!) but is a similar twist off method to the hot potato one and as you can see from the video below there is very little, if any, discomfort to the rooster.
When removing spurs it can be a good idea to have a bit of blood stopper and antiseptic cream / spray on hand (both usually available from feed/farm stores and similar places) and keep the newly de-spurred rooster (or butch hen!) separate from the other flock members to prevent them picking at the area where the spurs once were.
The above photo is of the spurs from Janice's Bantam Golden Laced Cochin hen "I noticed that she was walking funny, kind of having trouble. So I caught her up to have a look at her feet. What I saw was, she had 2 very large spurs! I have never seen or known a hen to have spurs. I used the pliers method to remove them. They came off very easily and without a drop of blood. I would suggest everyone use this method."
There are other methods of spur removal - including the use of hacksaws and the like (!) - but for me personally the ones mentioned above would be the ones least likely to cause any distress to the rooster or hen being attended to.