Wordpress Multisite File Upload Limit

I'm trying to change the File Upload Limit on my Wordpress multisite, which was 2MB. I followed instructions in a blog post - http://www.wpbeginner.com/wp-tutorials/how-to-increase-the-maximum-file-upload-size-in-wordpress/ and the limit shrank to 548kb instead.

Having changed it, you'd think I'd be able to figure out what made the change and how to increase it. But instead, I'm stuck at 548kb. I've tried to restore all the original settings and got nowhere. Am now really stuck! I need to correct this quickly. Help!