Annoying microsoft popup

I use windows 7 with internet explorer 11. Whenever I get onto the 'net, a very large and annoying blue, square popup appears on my explorer homepage, recommending me to upgrade to windows 10 ( I hate win 10, as it slows down my laptop). I click onto the X up in the right corner of the popup to get rid of it, and some times it disappears, other times it doesn't. How do I keep this very annoying popup from re appearing everytime I open up internet explorer?

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