iMac crashing daily, why?

Quite frustrated as to why my iMac (early 2009) is crashing everyday, sometimes twice a day. Here are the technical details:

Using OS X vs 10.8.5

Processor - 3.06 GHz Intel Core 2 duo

Memory - 8 GB 1067 MHz DDR3

Graphics - NVIDIA GeForce GT 130 512 MB

I read that upgrading the OS would help but I use Adobe PS CS5 daily and can not afford to risk having problems using

that software. I can not afford (financially) to buy a new computer right now and prefer not to use cloud software.

Also, keeping in mind that perhaps it might be a memory issue, when I am using PS or Firefox, I try to not use them both

at the same time but even that doesn't matter. And, it seems to happen when using either program, not one or the other.

Maybe I should stop using Firefox for awhile and switch to Safari? Perhaps that would help?

Finally, is it possible just to upgrade to a newer version (compatible w/ PS CS5) w/o having to go to El Capitan?

Any suggestions out there?

Thank you in advance ~