If you find an error like the picture above, hopefully this article will be one of the solutions and the solution is similar to this article.

Here are the steps:

  1. Login to Plesk, click Domain and click on the domain that is having problems, then click PHP Settings.
  2. Change post_max_size and upload_max_filesize to the desired size and click OK.

Before

After

  1. Try uploading the file again in WordPress.

Note: if the upload_max_filesize size is bigger than post_max_size, then WordPress will still follow the post_max_size size, in this case I changed both to 16MB.

You can see the upload file size limit by visiting the Media – Add New page, here are the before and after results.

Before

After

Please try and good luck, thank you.