[Tutor] How to solve a problem?

A printers@sendme.cz
Wed, 26 Dec 2001 18:40:58 +0100

My program downloads  regularly some files and it takes some 
time so I need to shorten this downloading time. As most of these 
files are the same, many times when the program downloads these 
files, I  would like to  download only those that are not the same or 
are newer. What is the best solution?
Many thanks for help.