Firstly, you need to download the new theme package from your Themeforest account. Once you have the new theme package, you can choose to upload the theme via WordPress or via FTP.
Step 1: Navigate to Insight Studio core >> Welcome
Step 2: Fill your Purchase code and submit. Then the template automatically updated.
Step 1: You need to deactivate the current Mitech theme in Appearance > Themes section by simply activating a different theme. Once you activate a different theme, you can delete the Mitech.
Step 2: Retrieve the Mitech.zip file from your new Themeforest download. If you download All files & documentation, then you need to unzip the archive file you received, the Mitech.zip file will be inside of it.
Step 3: Then simply upload and activate the Mitech file in the Appearance > Themes section like you've done when installing theme.