I tried to upload a collection of 3MB images to a site today and every one bombed out with the following error:
[filename] exceeds the maximum upload size for this site.
I googled around for an answer for a bit and then it hit me: the site's on WordPress multisite and I bet there's a setting. After a dive in the Network Admin area I found it. Head to your Settings and look for the following:
Max upload file size
I changed mine to 5000kb (5MBs). You may also need this WPBegginer article to reflect the change in your environment, or talk to your host.