My articles changed appearance after installing FLEXIcontent

A short answer:

-- To change apperance of your articles (now called items), go to Template manager and edit the item layout of 'default' template, simply drag and drop fields to remove or add them

A longer answer:

What is happening is this:

-- Joomla component 'com_content' is no longer used to display your content, instead now they are rendered by component 'com_flexicontent'
-- We will call articles as FLEXIcontent items,

-- Items are assigned to a FLEXIcontent item TYPE, and each type defines what extra fields each item will use in Edit Form and when it is displayed

So, to control what is displayed you do in 2 places

1. Go to "Types" (backend) and edit FLEXIcontent Content -Type- of your items (articles) on initial installation it is 'article', there you can see the template that you are using it must be 'default' by default,

- (if it is 'blog' (item layout) then you can disable some fields in parameters there too)

2. Then go to Template manager and edit the item layout of 'default' template, drag and drop fields to remove or add them