Q: Upgrading old imac

first time poster. please help - I am having trouble using itunes with my new iphone and I'm guessing its because my software is old and so can't use the newest itunes. However there are no software updates for me. Can I and if so, howdo I update my computer please? (without losing all my stuff)

Thanks for helping. This is my imac info...

Hardware Overview:

  Model Name:    iMac

  Model Identifier:    iMac9,1

  Processor Name:    Intel Core 2 Duo

  Processor Speed:    2.93 GHz

  Number Of Processors:    1

  Total Number Of Cores:    2

  L2 Cache:    6 MB

  Memory:    4 GB

  Bus Speed:    1.07 GHz

  Boot ROM Version:    IM91.008D.B08

  SMC Version (system):    1.45f0