Briefly, because it's not the place for this, if you make yourself an account on Photobucket and upload your pictures there, then it doesn't matter what size they are since you're linking to the Photobucket site instead of using the limited capacity of the forum page, which is why, I suspect that you're having trouble getting the photos the right size (unless you simply
want them smaller, and I suspect you can manipulate that aspect on Photobucket, too.)
1. Upload photo (there's a clearly marked button for this on the Photobucket page.) You can either use the file location option or drag and drop the pic from the desktop (or opened file) straight into the dotted area shown.
2. You'll see a loading bar filling up as the pic's uploaded. When it finishes a thumbnail of your photo appears, with an option to title it, should you wish to.
3. Click on the thumbnail photo. A larger version will appear and on the right-hand side you'll see four options under "share this photo." Click on the bottom one, marked IMG. You'll see the link button briefly flash yellow and it will say "copied." The link you need has been automatically saved to your clipboard.
4. Return to your forum post. Left click where you want your photo to appear, then right click and paste it in.
5. Congratulations, you've succeeded! Post your awesome, illustrated writings.
Edit - If for any reason it's still proving tricky and you don't want to look an ass on the forum, please feel free to PM me for advice.