A LITTLE DOUBT IN SYSTEM BACK-UP?

I used to download lots of data over the internet. I thought that its better to keep a back up of all my data. So, I manually copied all my 1TB files to my external hard disk. Once in every three days, I delete all the data on the external drive and copy everything from my system, in order to keep up with the changes and updates. Is there a better way to do this? Is there any software to just update the changes, instead of deleting and copying everything. If there is a solution, it would be godly and enchanting.