OSX Upgrade newbie: 10.5.8 to Snow Leopard, for better performance - whats required?

I've been looking into ways to totally clean out my mac and speed it
up. I then thought to upgrade to the later version snow leopard, as
ive run 10.5 on this MacBook since I got it years ago, and it seems a
logical move for improvement of speed/better functioning.

Can I ask what's involved in changing my os, ie will I need to back
up, and, unless I choose to restore everything, will it leave me with
a 'blank canvas' so to speak, with none of the old stuff thats on my
mac currently, therefore no need for the cleaning up of old files, log
files, repairing disk etc?

I'm sure there is a thread lurking in this forum all about this, I am just using the wrong search terms.. could someone post a link or help me out?

Thanks!

1. Buy a Snow Leopard DVD from Apple.

2. Back up everything to an external HD using Time Machine.

3. Boot the machine with the new Snow Leopard DVD, erase the hard drive, install Snow Leopard. During the installation you'll be asked if you wish to migrate data using another Mac or Time Machine. Select Time Machine. Attach your external drive with the Time Machine backup. It may take some time to restore.

4. Reboot into Snow Leopard.