Would it be a good idea to change my Sony viao OS from win 7 to Linux or (if possible) iOS?

Dual boot it! You'll need something to manage your partitions so it can condense the windows partition and open up room for a Linux partition. Once that is done take your preferred version of Linux and install it. It will see that you have windows already installed and should set up a boot loaded so you can choose which OS you want to use when you boot the system up.

Getting OSX running is a lot of a pain, but linux can help round out a machine (if you have need for 'more' without paying more). Most distros I have seen use installers that are comfortable repartitioning and building the area needed on an existing install.