The featured image on the mezzanine.blog.models.BlogPost content type is of type mezzanine.core.fields.FileField. When I try to upload a featured image there is a 2.5MB limit on the size of the file. Where is this value defined? I want to increase or remove this restriction.
This is the default limit imposed by django's FILE_UPLOAD_MAX_MEMORY_SIZE setting. Increasing that will solve your problem.
If one wanted to limit the size of FileField's to some value lower than the FILE_UPLOAD_MAX_MEMORY_SIZE, they can do so with the FILEBROWSER_MAX_UPLOAD_SIZE setting. There is no way to effectively set it higher.