Upgrading to High Sierra

Hello. I have OS X Yosemite 10.10.2. I have been trying for days to upgrade my mac to High Sierra. It's been downloaded from the App Store, but it never seems to install all the way. Today when I was trying (and I've tried repeatedly), it says "Recovery server cannot be contacted". I'm not sure what to do. Do I need to delete the Installer App and try re-downloading it and try again? Is there a way to make the installation go a bit faster? I've literally let it try and install for 18 hours straight with no movement. After it gets almost finished, it's sat there for hours upon hours! Can I clean off my mac somehow to make this process a bit faster? Please help! I am unable to open up files from my external hard drive that are from a newer version of Pages, and I'm assuming that upgrading will help me be able to open them or install a