On a default WordPress 4.8 install on PHP5 the default file upload size seems to be (at least on my install) 2MB. If you’re uploading large image files or videos, it’s likely you’ll want to upload files much larger than this.
There’s a number of possible configuration locations that can control/configure the upload size. The first location is likely to be your php.ini file used by your apache or nginx. The settings to increase are:
- post_max_size (must be larger than upload_max_size)
This article has a comprehensive walkthrough the possible configuration changes.