When trying to upload a theme from Prestashop admin panel, you receive an error below.
QuoteThe uploaded file exceeds xxM
It is because upload_max_filesize in your php.ini is set to a value lesser than your actual theme size. Simply, increase upload_max_filesize & set it to higher than your theme size (right click on the .zip file of your theme to know the size).
After increasing the upload_max_filesize value, try uploading your theme. It will upload successfully.