If your current isp offers free web-space why not download your site or use the copy you have on your hard drive (you do have a copy from when you ftp'd it, don't you) and put that on the new isp web-space. click here
If you don't use your Orange account by dial-up then it will eventually locked. It can be unlocked but the only way Orange can run your site is getting a slice of the dial-up phone bill. It would be better in the long run to transfer your site as terryf has said but even better would be to get your own domain name and host it with a provider and then it doesn't matter which ISP you are with and you don't have to worry about the url changing. However this option is not free.