This is a VERY common question :-(
I wish I had a dollar for every time I have seen it.
One quick search on YA alone yields hundreds of instant responses - no waiting!
I'm sure you'll find something to your liking amongst all this:
http://answers.yahoo.com/search/search_result;_ylt=AlhBObSzRujWLJZAagaj1mcjzKIX;_ylv=3?p=photo+editing+
Just in case that didn't get you what you wanted, you can always try here, as well: http://lmgtfy.com/?q=image+editing+programs
However, it makes much more sense to have a decent editing program on your computer (they work much better), instead of having to upload every single photo, work it, then download it again. In the end, you actually do a lot more up/downloading than you would for a resident program. On top of that, if your internet is down, you have nothing.
If you can't afford Photoshop, look into PS Elements, or download Gimp (which is free).
P.S. There was no need to repeat this question a minute later!