In order to update the theme manually, follow the next steps:
Please, make sure, that you updated your WordPress to 5.5 versions.
Before, the only way to update was to use FTP client to upload the new version. WordPress 5.5 has fixed this problem and now you can simply go to the Appearance > Themes > Add New page and upload the new version like you would upload any new theme zip file.
After that click on the Upload Theme button to upload your theme zip file. WordPress will automatically detect the existing theme and will give you the option to ‘Replace current with uploaded’ version.
To have the possibility to receive future updates, please, go to TopTen License section and enter here your license key