Themes updates

Hi,

I saw on my Dashboard> Updates that three of the Themes (Twenty Fourteen, Twenty Thirteen, Twenty Twelve) have new versions available. I did not update them because I am afraid to loose any customizations that have been made to theme files, as I do not know how to use child themes. I would like to know if I should updates them, and if you would be able to help me with that.

Many thanks.

Best,
Léa