How to see Background options with 5.4.1 version ?

Hello Guys Now I can only settle the parameter once, and no way to apply modifications Any ideas ? Thanks

Background can be set through the Appearance panel > Background. There you can add images, set the color or add gradients. Everything is editable. Not sure what you mean by...

I can only settle the parameter once, and no way to apply modifications

I see no limitations. You can also adjust your background directly by writing CSS rules.