To do this, we need to use the distributive property. The distributive property allows the outside number of a parenthesis to multiple all numbers within the parenthesis. Let's use this formula and break it down.
-2n(4n-2) = -2n(4n) + -2n(-2)
-2n(4n) = -8n^2
-2n(-2) = 4n
Our expression is now -8n^2 + 4n.
I hope this helps!