How can I know if a remote file has been updated?

I want to know if a remote file (such as: http://www.diychart.com/1.txt) has been updated. how can I do? Thanks!

I imagine there are two ways:

1. Get the date of the remote http://www.diychart.com/1.txt, and compare the date with previous date

2. create a MD5 value based the remote http://www.diychart.com/1.txt, and compare the MD5 value with old value

I don't konw if the two ways are correct. I'm a beginner of C#, I don't know how to write code to perform the two ways.
...