Upgrade the Ubuntu OS to 18.04 for use on Raspberry Pi

I have an existing UbuntuMate project to bring Bsic Computer Skills to unemployed young people in rural towns and villages in South Africa. One of th eplatforms we have developed for delivery of the traning is cased on UbuntuMate running in RaspberryPi workstations. The original trainng content is due for an upgrade and I need to also upgrade the version of UbuntuMate from (about) 14 to 18.04, the current version that is compatible with the Pi. Because of the gap between versions a new bootable version of 18.04 needs to be created, the upgraded content added and from that a new .img needs to be derived for copying on to the 16Gb micro SD cards. I have the UbuntuMate .img from which to start, plus my 'old' .img, plus a file containing the updated training content. I also have a link to the suggested way of doing this,but I don't have the experience to actually do it! I would like to preserve the setup info from the original. I should mention that the model involves creation of an Apache localhost, because although the content is all held locally, the registration and scorekeeping happens in our server in the cloud. Here's the description: [login to view URL] Oh the other thing to bear in mind. We may need to create two distributions to cover 32-bt and 64-bit Pi's, since we have older hardware out there as well as the latest Pi going out now. Thanks, happy to add any further info if needed, as well as to test any output in the Pi environment. Looks like to source files are too big to upload to your website. Are there alternative upload options I could use?