I read an article online the other day–I forget what about–that used the prefix “uber”, saying something was “uberawesome” or the like.  I see this pretty often, mostly by literate folks who are trying to sound smart.  To borrow from a worn out internet meme, you’re doing it wrong.

Because I like good writing and good spellng (sic), please be advised that the correct spelling is “ueber”. 

It comes from the German prefix “über”, meaning over, or super.  It is pronounced not like “oo” as in “zoo”, but rather somewhat like a surfer bro saying “dude”.  To break it down, first say “oo”.  Now say “ee”.  Now put them together: your lips go “oo” while the middle of your tongue goes up as if to say “ee”.  That’s how you pronounce Ü. 
The same method is used for pronouncing the German Ä and Ö as well.

As for the spelling, it’s “Ü”.  But if your keyboard is missing the ü key, just substitute with “ue” and it is still correct.  The reason for that is because the umlaut (those two little dots) was merely a shorthand invention of monks, those scribes from the medieval times.  For that reason, it is not uncommon to see on old-timey looking signs the Ü written as an u with a little sideways e over it.