struggling to update software on my macbook

I don't understand your question very well, but it looks like you want to go back to Yosemite from Snow Leopard.

First of all, do you have a Time Machine backup you made in OS X Yosemite? If so, it's as simple as restoring that backup. To do it:

1. Plug the external drive with the Time Machine backup.
2. Hold down the Alt key while your Mac is starting up, and choose your external drive to boot up from OS X Recovery.
3. Choose the option to restore a Time Machine backup and follow the steps.

That option will erase your hard drive and will restore all the data from that backup.

If you do not have a backup, you'll have to upgrade to OS X Yosemite:

1. Go to Apple menu -> Software Update and install all updates available.
2. After updating Mac OS X, open the Mac App Store, go to Purchases and download the OS X Yosemite installer (if available).
3. The installer will open automatically when the download finishes, so follow its steps to upgrade Mac OS X.

You have the option to upgrade to OS X El Capitan instead (the latest stable OS X version), if you want to. You can download it from the Mac App Store for free.

If you don't have a clone backup it's time to start. Just like a seat belt and an air bag protect you in different ways when driving, you need both Time Machine and a clone for full protection.

Clones can be used to restore and are much quicker than Time Machine. You can also boot from your clone and be back to where you were before the problem started.

Create a Clone backup:

A clone is an exact bootable copy of your internal drive. Unlike standard copying of all files to another drive, the clone software copies hidden files along with other in-use files that are not available when you copy over files to another drive.

Software used to Clone:

SuperDuper! http://www.shirt-pocket.com/

CCC http://www.bombich.com/download.html

If you have updated to 10.6.8 and are unable to restore from Time Machine, go to the App Store Purchases tab and download Yosemite. Once it is installed, access your Time Machine backup to recover your data.

You are in a pickle....

Updating from 10.5.8 to 10.6 was not free. It requires a CD to install. At some point you must have purchased the installer.

I suggest you take the MacBook to an Apple store and have them install Yosemite or El Capitan on your drive. You can then use your Time Machine to restore your files.

Link to buy the DVD.

Snow Leopard Purchase

Use the combo update to save time in Software Update.

10.6.8 Combo Updater

You can then update to a higher OS using the App Store.