How to access label in default.aspx from another?

Hi,
In my default.aspx there's a label, then I am using an iframe which src="page1.aspx". When I click on the page1.aspx, I want the label text to change according to some click events on the page1. 
I need help on that.  Been stuck there for more than 1 day and can't progress further.
Thanks!
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