Always keep backup before update:
Update : Important Considerations : Read More

1. Download updated theme zip

Download updated theme file from the account you have used to purchase theme.

2. Install and activate ‘Easy Updates Manager’ Plugin

• Go To : Plugins > Add New
• Search for : Easy Updates Manager

  For more help related to plugin : Plugin direct link

• Install and activate plugin.
• Now further process is exact similar as we do while installing any fresh theme.
• 1. Go to Appearance > Themes.
• 2. Click the “Add New” button at the top of the page.

  
• 3. Click the “Upload Theme” button at the top of the page.

  
• 4. Browse for the updated theme zip file you have just downloaded. Click the “Install Now” button.

  
• It will give remark that theme is already installed.
  Click on the button : Replace active with uploaded

  
• It will auto activate theme once updating is finished.
  Activate if not.