Need help editing photos to upload to web

I am new to Apple and have never (even in my PC days) successfully attached a photo to an e-mail or website post. I have photos of a custom bicycle that I took with my Nikon digital camera. I plugged my SanDisk card reader into my MacBook Pro and the photos loaded into my IPhoto gallery with no problem whatsoever. The website I would like to share my photos on, www.roadbikereview.com provides a little tutorial as to the method of uploading photos with a new post on the board. The writer of this tutorial warns that virtually every photo has to be edited with computer software to less resolution in order to successfully upload. I played around in IPhoto for half an hour and see nothing that allows me to reduce the pixel count in order to comply with the 600 pixel maximum advised as do-able on this particular website. I then tried to upload the photos without editing and though I located them on the computer and tried to upload per the website's directions (but without editing), sure enough, no photos uploaded. I have no doubt it was due to file size (resolution setting-pixel count). Help please? There must be a native photo editing application that came with my '07 MBP right?

 

Thank you!!!