Easy: less need for sleep. I've been sleep deprived for about 60% of the last 6 months because of school. If we reduce the need for humans to sleep by, like, 2 hours so that we only need 6 hours of sleep to get a good rest, I wouldn't have to deal with this stupid physical and mental fatigue. I think that it'd be beneficial for people other than myself, as well; there's only a certain amount of time in a day, so reducing the amount of time we need to spend sleeping will increase the amount of time we have to do things. More things would get done in a shorter period of time.
This one may be a bit controversial, but I'd also either decrease fertility rates, make it more difficult to conceive a child or decrease human inclination toward sex. The population is growing at an extremely unsustainable rate and measures should be taken to at least stabilize it. Not like the friggin' Krogan genophage which almost wiped out the species; I mean we need to severely decrease the net growth of the population in order to stave off the inevitable depletion of resources for long enough to use science to discover ways to PREVENT the depletion of resources. I like the last one the best, though it may be the least effective, because I think that sex is too intrusive in our world; I would like to be able to watch television or walk down the street without being bombarded with sexual messages. Don't get me wrong, I don't make a big deal about it. I just ignore it, but I just wish that I didn't have to.
I would also like to make less of the population pants-on-head stupid. I'm hesitant to use the word "retarded" to finish the quote, though it would be nice to lower rates of mental disability, as well. I just wish we had fewer people doing stupid things in the world I wouldn't just reduce the amount of stupid people, though; needlessly selfish and/or aggressive people are completely unnecessary in society. While aggression and selfishness may have had uses for survival in the distant, distant past, they're outdated. These kind of people are why people "lose their faith in humanity". "One bad apple spoils the barrel", as they say, and I think that there should be fewer "bad apples" to spoil things for everyone else.
I also like the OP's non-smelly sweat suggestion. I hate the smell of sweat, but I realize that it's a necessary part of body temperature regulation in humans. Taking away the smell would be the most logical solution.