How often should I switch pairs of contact lenses?

I have six pairs of contact lenses that should last me the next year. I wore one pair of contacts for almost four months without any problems, but now that I have these six new pairs, I'm wondering if I should just switch them every two months or should I just keep wearing the one pair until I feel the need to switch them out? Does it make any kind of difference? I have really healthy eyes and no problems with my contacts up until now, but this is the first time I've worn contacts (save for that first trial pair), so I am a little green when it comes to this stuff.
In most cases, the disposable contacts are made of the same material as long-wear lenses. They are just packaged differently. As long as you keep your lenses clean and enzyme them regularly, there should be no problem. But if you start to develop any irritation, toss them and leave the contacts out until it is completely cleared. Also, do not switch brands of solutions while wearing the same pair of lenses. If you want to switch, toss the old lenses, and use only the new product on the next pair. Switching solutions midstream will not hurt your eyes, but the chemical reaction of the different solutions can damage your lenses. As always, for best results, do as your optometrist recommends.

i also keep my disposable contacts for 4months or more, altough it says on the box that you should dispose of it after a month, wearing it for an extra couple of months didnt really do anything harmful, they still worked, and i got to save money! =D
but i suppose it's wise to throw them away at their prescribed time, you might get eye infections or have problems bec the contacts youre wearin are past their expiry date.
ps. why dont you switch to extended wear instead of buying too many pairs of disposable ones? extended wear contacts can last a year without having to change them, so you save more in the long run =)

If your eye doctor told you to switch every 2 months, then you should do it. If you leave them in longer you could start to have problems with your eyes. You should also switch lenses if they start to bother you or get rips in them before the 2 months are over.