Performance-wise...get as light as possible without losing strength or health.

Are you a guy or a girl? Girls need to have more body fat than guys do to be healthy. An online calculator isn't going to be very accurate, but an easy way too tell is if you have flabby stuff where you don't want to have it. If you decide that you DO want to lose weight, the best (and safest) way is to figure out your basal metabolic rate and how much you burn working out, then create a diet (all the normal food you eat already....assuming that you're eating healthy) that's at a 500 calorie deficit.

If that's too tricky, just eat so that you always feel slightly hungry, but don't starve yourself. If you get sick, you're not eating enough. If you don't lose weight, you're eating too much. Be careful not to lose more than 1-2 pounds per week.

Good Luck!!

Another helpful trick is to eat more but smaller meals to loose weight. The opposite holds true to gain weight. Currently I try and eat about 6-8 meals per day, though some of those "meals" are just a handful of peanuts or almonds and a handful of raisins or soemthing like that.