Oracle

I have a field in my database that is 100 characters long. I want to change characters 50, 51, 52, 53, 54 as follows:

currently: 2345U 7834U
want: 02345 07834

Essentially I’m trying to get rid of the end “U” and put a zero on thefront of the number. I need to do this generically as I have about 400 records that require this change. In other words, each of the 400 occurences could use different numbers (though they all end in U and I want to drop the U and put the zero in front).