Deleting/Editing a line in a file.

Question

Hi all, I'm new to .NET C# and I have a challenge to delete or edit a line from a text file which contains 1000 lines. How do I check for the position of the line? And is the a replace method I could use do replace this line with a new one? Currently I search for a line I want to manipulate using Regular Expressions. All I need to know is how can I replace that line?