Hi.
In your question you are talking about manipulating table_names, but in your examples you seem to be manipulating column names. The following code will perform the actions shown in your examples:
BEGIN
FOR c IN (SELECT table_name, column_name
FROM user_tab_columns
WHERE column_name like 'U##%')
LOOP
EXECUTE IMMEDIATE 'UPDATE ' || c.table_name ||
' SET ' || c.column_name || ' = UPPER(' || SUBSTR(c.column_name, 4) || ')';
END LOOP;
END;
/
If I've missed the point please clarify the question and I'll have another go 
Cheers