Note : Its always recommended to backup your Website, Theme, Database before updating. You can use this updraftplus plugin to have regular backups of your Website.
Updating the theme is very easy.
You can go to Appearance / Themes and you will see a notification to update theme if you have entered a valid purchase code in Themeoptions/Welcome screen.
After updating the theme, just go to Appearance->plugins to update all plugins to their latest versions.