Ok
Click on Save for Web.
There will be a screen that pops up with like 4 different windows of the picture.
If you look below the picture there will be the size of the file.  Photoshop does this automatically, but you can change the settings on any of those 4 pictures.
On the right side is a bunch of tabs/buttons.
There is a tab of which kind of image you want to save it as, just use jpeg.
Underneath the Jpeg tab is a overall quality tab, experiment by changing them and then look below the picture window and the size of the file will change as you mess with the settings on the quality tab.
Right next to the general quality tab is a "Quality" tab that you can open and then adjust by sliding it either back or forward to make small adjustments on the picture.  As you change this, the size of the images will change below the picture windows if you look closely.  Adjust all of these setting until you get the desired look by looking on the 4 windows.
So, Click on the window you want to adjust(Photoshop gives you four general options and the sizes of the file differ) and adjust as needed using the methods I listed above and then save it.