To updating the theme there are 2 ways.
When there’s a new update released you will get notification on your dashboard. You can simply update from there.
When there’s a new update available on Themeforest. Download the new updated theme. Then extract and upload new version from your dashboard Appearance → Themes. Then activate the theme. During this process, no data will be lost. Because all pages and posts data saves in Database.
After activating new theme, you needs to check that if there’s any update available for ShadePro theme support plugin as well by visiting this page Appearance → Installed Plugins.