I did have two plugins with the original course in version 1.9.5, one was the "book" plugin and a "feedback" module. I do mention this briefly in the "Starting steps" section. The book plugin has to be installed during each upgrade until 2.3 as then it is included in moodle. Download the plugin for each version of moodle. After uploading the module directory structure to your server, then move the plugin to the appropriate directory (per the plugin install instructions) and then after the upgrade of moodle is done and you login, go to the Site administration and see if there are any configuration settings that have to be addressed. For the book plugin I had to do this for each version but once you get to 2.3 you don't have to deal with it anymore. The feedback module I was using wasn't maintained after 2.0 and so I just dropped that and recreated this one with the new feedback module in 2.4.1
If you are this far back like I was there are going to be some issues where a plugin or module may have limited upgrades. By the time you get to 2.4.1 you will find a much better presentation with a lot more plugin and module options built into moodle by default which is really nice.