getting alerts my browser needs upgrade. I must upgrade ios to get updated browser. What are the downsides to upgrading ios?

I have a snow leapord ios which allows safari 5.1 as the "latest" browser. Many of the sites I visit are asking me to upgrade the browser. Looking into this I found that I need to upgrade the operating system first and I want to be sure that I can do that without losing anything that is currently on my desktop. What should I expect when doing a ios upgrade, and will that include the safari upgrade as well or is it a separate task. Thanks