Windows 7: Best external to external hard drive synchronized backup plan?

So I want to clone one external 2TB with another. So one drive is the main use one and another the backup one. So I copy everything over to backup and i store the backup at another house and then I start using the main: deleting and adding/editing files. What is the best software or whatever to allow me, after some time, synchronize/clone the externals again without deleting all on the backup drive and recopying? (main to backup) and make them clones again? ..Adding and deleting or replacing any nonidentical files.. Like where i can press a button on some software and it do the work for me.
Sorry if this is confusing

There's a bunch of applications that can do that.

They all work pretty much the same way, but would differ in how easy they are to understand and configure---the interfaces would differ and the help files would differ.

I use FreeFileSync from sourceforge.net.

Others are Syncback, Folder Clone, Karen's Replicator, FBackup, Second Copy, and Synchromagic.

You should be able to configure them to do one or the other of the following:

1: If you delete or modify a file on the "original", it will also be deleted or modified on the backup.

2: If you delete a file on the "original", it will be retained on the backup. If you modify a file, both the modified and unmodified file will be retained on the backup.

It's up to you which choice you prefer. I use the first method, which is often called "mirroring"--one drive is an exact match of the other.

Another vote for FreeFileSync

Green Elephant,
Windows 7 Home Premium already contains SyncToy. I've been using that for very similar purposes over the past three or four years with absolutely no problems whatsoever. It's simple, free and does the job.

You sure you aren't confusing SyncToy with Sync Center? They aren't the same. I have Home Premium on two machines and neither have SyncToy.

I use SyncToy too, but it does not come with windows. It is a free download from them though. Download SyncToy 2.1 from Official Microsoft Download Center and a tutorial on how to use it SyncToy - Backup User Data

Sorry - put it down to age or something!
Essenbe is quite right and I must have forgotten having downloaded SyncToy ages ago.

It doesn't matter who is right or wrong, either way it's a good program and will do great for what I understand the OP wants, I've used it for years. Best of all, you can't beat the price.....Free. Free is always a good price.