You can find a high level overview of what's new in each version on http://help.qlik.com/ . Go to the Qlik Sense section, then search 'what's new' for each version; you can change the version by using the drop down menu in the top right.
You can also take a look at the release notes for each version on the downloads page. You can access the downloads by navigating to Qlik.com, then logging in. Once you are logged in go to the 'Services' menu, and choose 'Customer Downloads'. Once you are on the downloads page, select the version you want to look at, then choose 'Release Notes' under File Function.
Hope that helps!
All The Best,
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