Your ISP normally offers you free web space and a few other places will give you free space too.
First port of call should be your ISP, but free web space provided by an ISP sometimes does not allow FTP. Some ISPs prefer you to use their own upload control panel page.
You do not 'convert' a site to FTP. FTP stands for File Transfer Protocol and is a method of moving the files from your computer to its home on a web server. You can get several free FTP programs and most good web editing software has FTP built in, negating the need for a third party FTP program.
3 megs is not a small amount of space. HTML files are tiny and any images should be optimised for fast downloads. You could easily cram 40 or more web pages and 20 images into 3 megs with room to spare. My main business site is 29 files in three folders and comes to a vast 259kb, just over a quarter of a meg.
Start with your ISP and ask if you get any free wen space with your internet dial up/broadband account and if you do ask them what your FTP details are. They will help you with your username and password and you're off.
Any problems and you know where to come for help.