Sense the 3 difficulty levels are raid finder,normal,heroic.I need to know how to change the level from raid finder to normal.
You just don't use the raid finder. You instead form a group of 10 or 25 on your own and all walk to the entrance to dragon soul. That would be normal mode. Heroic you have to unlock.
Random groups have very little coordination, so they are only able to do the easiest difficulty. Normal and heroics are significantly harder which requires a dedicated guild learning the fights from week to week.
'raid finder' itself is separate from normal/heroic so you dont have to...its done automatically. to chane beteen normal and heroic, right-click your protrait in top-left and look for 'raid difficulty' tab.