Follow these steps below to install Manta theme via FTP:
Step 1. Login your FTP account via FTP software to access your host web server.
Step 2. Extract manta.zip file.
Step 3. Upload the extracted folder manta to wp-content/themes folder.
Step 4. Activate Manta theme in Dashboard > Appearance > Themes.
Step 5. Install and activate Thim Core plugin of Manta that required for importing demo data.