1. Log in to cPanel and navigate to Select PHP Version under the Software section.
2. Click Switch to PHP Options in the top right corner.
3. Locate the upload_max_filesize setting.
4. Click on the value next to it and increase it (e.g., set it to 128M or higher).
5. Find and adjust post_max_size as well, ensuring it’s equal to or larger than upload_max_filesize.
6. Click Save to apply the changes.

Once updated, you should be able to upload larger themes and files without issues.