“You might have to refresh your browser.”

You are helping a person log in to a website account. He has entered his login name and password, but the screen just turns white and nothing happens. You want this person to re-load the page, so you tell him this.

You might have to refresh your browser.

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(someone) might have to (do something)

This is a polite way to suggest that someone should do something. It can be used when you are trying to give a suggestion for how to do something but don't want to sound too bossy. A more straightforward way to say it, which could be used with family or close friends, is:

You have to refresh it.

refresh (a web page)

This means to re-load a web page by clicking one of the buttons at the top of your web browser. Pushing the button causes the software to download the information from that website again. The word "refresh" can also be used as the name for that button:

OK, now click "refresh".

a web browser

This is a computer program like Firefox, Safari, Internet Explorer, or Chrome that you use to look at the Internet. The complete name is "web browser" but it can also just be called a "browser".