Several of us have posted instructions lately, so I'm not sure which post you mean.
Whatever picture editing software you using, simply open your picture in that program, and look for where you set the image quality. Most times, it will be defaulted to 72 dots per inch (DPI). If you lower this to somewhere in the 60s DPI, you should be able to get the file down to around 96,000 bytes, or 96K which is actually almost 100,000 bytes in reality and can be posted without losing size.
If you're using Adobe Photoshop, simply click file/ save for web, and set reduce the quality until you see that it is less than 100K.
If you click on my name, then send a private message, tell me the name of the program you're using, I'll try to tell you exactly where to go to find what you need to do.
John