Migrating from Joomla 1.5.x to 1.7-Collection of common programming errors

You will probably need more disk space than you have available. Your current site, plus the downloaded zip file, plus space for extracting the files plus any backups you have on the server are likely to exceed your 100MB.

I’d recommend taking a backup of your site, setting up the site on a localhost (xampp, wamp, etc) server on your own machine and run the migration there. This will have the benefits of not hitting arbitrary limits of what sounds like a very low budget web host.

Obviously you’ll have the extra complexity of setting up your own server on your PC – but there are many tutorials out there that will walk you through the process, and the learning of new skills is always good.