Older Imac upgrade

Hi,

I am looking for information about updating my iMac to the new el capitan version. Currently I have os x 10.6.8 and I'm not sure of the year of my iMac. I came across the fact that I cannot update my itunes any longer, so it is not compatible with my new iphone, but I put that on my windows laptop. Now my printer has died and I have not been able to find a printer that is still compatible with my 10.6.8. So I am looking in to upgrading to the new el capitan version. Will this fix that compatibility problem? Is my iMac even able to be updated? I am concerned something may not work after I upgrade, such as my new itunes will not be compatible with my iphone 5c any longer. Or my version of pages, or iphoto. Will I be in danger of losing my pictures? If any of that happens will I be able to revert back to way things were? Should i try to do this on my own, or am I able to take it in and have them do it in the store? haha! Thank you! I hope someone is able to help.