Currently, NSU is offering version EN21 for free licensed download. You must update it to the most current version on both PCs and Macs. It is not advised to install previous versions. You can also sign up for the free EndNote Online version, which can be synced with a desktop library or used on its own.
(The desktop software cannot be installed on Chromebooks -- but you can use the online version)
Do not save the EndNote Library in the iCloud!
If you have an existing EndNote Library: Before upgrading your computer, make sure you back up your EndNote Library on a compatible external hard drive and sync your desktop library to the online library. If you don't have the EndNote Online account yet, create an account, connect to the library on your computer, and run the sync function.