This is the way I do it (there is another way involving "save for web" but I never use that):
After you finish all your edits save your image -- this is your original and you want to save a full resolution version.
Now, click
Image > Resize > Image Size. This screen will open up. Check all three of the blocks in the lower left corner; your screen will look like this:
- Resize-1.jpg (102.24 KiB) Viewed 1824 times
Now, up in the top section, overtype to change the
longest side to "500". This happens to be a square image so it doesn't matter which one you change. All of the other numbers change in proportion (that's why you wanted all three of those lower-left corner blocks checked). The screen changes to look like this:
- Resixe-2.jpg (83.53 KiB) Viewed 1824 times
Click
OK and you are done.
Now File > Save as...
This is important, you want to save as "new filename". If you don't do that you will overwrite your original, high resolution file with this new small file. This is the file you want to upload into your forum post. The longest side is 500 px or less.
Rusty