Updating 10 4 8
If you have a good backup, then data loss shouldn't be an issue. Before embarking on a major OS upgrade, it would be wise, advisable and very prudent if you backup your current system to an external connected and Mac formatted Flash drive OR externally connected USB, Thunderbolt or Fire Wire 800, Mac formatted hard drive.
Then, use either OS X Time Machine app to backup your entire system to the external drive OR purchase, install and use a data cloning app, like Carbon Copy Cloner or Super Duper, to make an exact and bootable copy (clone) of your entire Mac's internal hard drive.
If you previously downloaded the last i Photo update (which is no longer available from the Mac App Store), then i Photo continues to work with Yosemite and you can choose to continue to use i Photo instead of the new Photos app.
If you don't have the last update of i Photo, any other version of i Photo will no longer work with Yosemite. Does that mean I can't run OS X 10.8 Mountain Lion? Not sure what specs are relevant but it's a white, early 2008, Mac Book 4.1, model MB402LL/A. The reason I ask is, it's running poorly, VERY poorly. And I just can't afford a new one or an expensive tech 'overhaul'.
In OS X Snow Leopard, If you go into the Finder Preferences, and make sure in the Devces list, make sure hard disks, Extenal disks and CD/DVDs are all checked, you should be able to see your El Cap partition or drive and access it from OS X Snow Leopard.
An update to the PS3™ system software was released on August 28, 2019.
As for losing data, you should be backing up on a regular basis...
If you have a good backup, then data loss shouldn't be an issue. If you did not previously purchase Mavericks from the app store, then you can not upgrade to Mavericks at all any more. I don't see what "installing the complete System new" has to do with anything at all...
So again, my machine (as it stands) really won't run 10.8? Thank you in advance for any help you would offer, Scott I think I did a very good job explaining how to do a backup and you REALLY should have/NEED a backup of your computer if you have important data that you can't afford to lose. The first paragraph covers the backup options and details pretty well. Computers and hard drives CAN and DO fail at ANY TIME and at the worst possible time! Your year and model Mac Book is runnng the latest OS X version it can, 10.7.5 Lion. If your Mac Book is running slow, run etrecheck diagnostic app and paste its output here in another new thread.
You can use this update to upgrade your system software to version 4.85.
If your PS3™ system software version is 4.85 (or later), you do not need to perform this update.
This step is really needed in case something goes wrong with the install of the new OS or you simply do not like the new OS, you have a very easy way/procedure to return your Mac to its former working state.
Then, determine if your Mac meets ALL minimum system install requirements.
Once you have determined all of this, you should be able to find the latest versions of OS X by clicking on the Mac App Store icon in the OS X Dock and then login to the Mac App Store using your Apple ID and password and if you purchased a download code, input that code.