The intermediate paths mostly call for an older version of Mendix than you have your project in now (9.18).
It is not possible to convert from the newer version back to the older version.
So you have 2 options:
1- Continue working on the learning path with the newer Mendix version (this will work and additional documents that are provided can be converted to the newer version)
2- Download the older version and create a new app for the path that you are currently following in stead of opening the app from the newer version.
My choice would be to use the newer version and see what issues you run into as these are the points where you probably learn the most.