Mac software update gone wrong? Please help

Hey guys. New to these forums. I am here regarding my Mac desktop. I am having troubles with doing a software update. I have had this mac for about 5 or more years. It is running on 10.6.8. I really have been wanting to upgrade to Yosemite, but I wanted to back up my Mac first. So I went to time machine and it said I needed to do a software update to set it up with time capsule, so I let it scan for software updates and pores see ok and let the software updates download, when it finished it told me I had tore start my mac. So I did. I did that at 11 last night and it is still "restarting". Did I do something wrong? I am very confused. I don't know what to do. I just want to upgrade to yosemite, what should I do??? It has been in the purple galaxy loading page since last night.

 

Any one know what to do