File uploads

General settings
WIDTHxHEIGHT
The maximum allowed image size (e.g. 640x480). Set to 0 for no restriction. If an image toolkit is installed, files exceeding this value will be scaled down to fit.
Display attached files when viewing a post.
Default extensions that users can upload. Separate extensions with a space and do not include the leading dot.
MB
The default maximum file size a user can upload. If an image is uploaded and a maximum resolution is set, the size will be checked after the file has been resized.
MB
The default maximum size of all files a user can have on the site.

Your PHP settings limit the maximum file size per upload to 64 MB.