This free tool should work...
Easy Graphic Converter: free image converter, graphic converter software.
You should be able to specify the level of compression. Bear in mind that the higher the compression settings, the more distorted the image becomes.
There are a few things you can do to reduce file size without distorting the image too noticeably.
- Lighten the image by reducing contrast.
- Blur unimportant parts of the image.
- Remove unimportant elements by cropping the image.
Overall, an image that is not sharply focused and that doesn't use vivid colours will be much more easily compressed. If the background is not a crucial part of the image, you may want to remove it so that you're only including the focal point.
Good Luck!