Q: Should I upgrade from Snow Leopard to El Capitan?

https://discussions.apple.com/docs/DOC-6271 should be read before you proceed

Oui, je te conseille de passer a un système plus récent ( Yosemite ou El Capitan )

les fonctionnalités ont toutes été améliorées

Il faut déjà préparer son changement en sauvegardant tous les fichiers personnels précieux dans un volume externe ( en cas de problème , car le système pèse 5 Go )

Aussi aller voir des vidéos pour voir exactement comment il faut faire .

J'espère t'avoir aidé.

I would encourage you to upgrade—it never pays to get too far behind in the technology or the OS X. It won't be long and 10.12 Sierra will be released and you are just that much further behind.

OS X El Capitan - Technical Specifications

You may be disappointment in performance if you do not have 8GB of RAM.

Always have a backup in the case you need to fall back for any reason. How to create a boot clone

Staying current is the best way to insure system security.

In short, you should upgrade. Why? Apple is no longer providing security updates past, I believe, Mountain Lion.

As others have pointed out, make sure you have access to older software or tested solutions to replace it.

Check to make sure your applications are compatible. PowerPC applications are no longer supported after 10.6.      

Application Compatibility

Applications Compatibility (2)

El Capitan 10.11 Compatibility information

Also check to make sure there is a compatible driver for your printer.

Do a backup before installing, preferable 2 backups on 2 different drives.

One option is to create a new partition (~30- 50 GB), install the new OS, and ‘test drive’ it. If you like/don’t like it it, you can then remove the partition. Do a backup before you do anything. By doing this, if you don’t like it you won’t have to go though the revert process.

Open Disk Utility, select your hard drive (step 1), then the Partition tab (step 2), and select the partition. Using the /// at the bottom move it up (step 3) until the size box decrease by about 50 GB. Select the newly created space and hit the + button (step 4). Name it something and select Mac OS Extended (Journaled) as the format (step 5). Then hit the Apply button(step 6). Download the installer from the App Store and when it starts, point it at the new partition. You might want to make a copy of the installer outside the Applications folder to avoid having to re-download it in the future. Once installed, restart with the option/alt key held down, select the new partition and reboot. Test away.

You are welcome.