What's the best way to lower the resolution on an image thats going to be part of a webpage ?

Yeah its the actual size of the image, so just enlarge/reduce it, and save uder a different name, theres some slider thing when you save a jpeg for compression, just ignore that. You can adjust the compression to optimize things, mainly use this to get even smaller file sizes. The size of the displayed image is define by HTML/CSS properties,not the actual image size.