There are several ways of controlling file types and sizes that members can upload.
First, you need to manage the Global List of file types allowed site wide: Pencil Tool > Administration > Moderation > Filtering and review the options for File Validation.
Individual content types may limit this list further but for file types to be allowed on your site they must appear on this list.
You can also limit the files allowed within specific content types by going to Pencil Tool > Administration > Applications > Content > Content Type] > Filtering and reviewing the File Validation options.
Media galleries also enable allowing/disallowing specific file types within each specific media gallery. For example, if a media gallery was intended to only host images, it could be limited to only allow image file types. Individual media gallery options can be set by going to the media gallery, and selecting Pencil Tool > Manage Gallery > File Options and adjusting the allowed and restricted file extensions lists: