First of all, you need to download the theme installable file from your account that purchased item, go to your ThemeForest Account > Downloads Tab
Now go to your site Dashboard > Appearance > Themes and click on Add New Theme like below
Now click on Upload Theme
Choose the zipped file that you have downloaded from ThemeForest and click on the Install button, then wait for the installation process
Final step click on Activate theme
Sometimes, for some issues, you won’t be able to upload the Theme via WordPress Dashboard>Appearance>Theme>Add New>Upload Theme>; That time, you can try via this way.
Go to the cPanel (https://yoursite.com:2083 or https://yoursite.com/cpanel)
Navigate to the File Manager>public_html/wp-content/themes/, then click on the “Upload” button from the top section of cPanel.
Log in to your server via your FTP software ( FileZilla, Transmit, etc )
Unzip the Kidstore .zip file, ONLY use the extracted theme folder.
Upload the extracted theme folder into wp-content > themes
Activate the newly installed theme by going to Appearance > Themes
Go to Appearance > Install Plugins and install all required plugins
Simply click the Install button on each plugin to install them