The Step Up is a II Chord; it is one full step (half step + half step) above the root chord (I).

What is the Step Up in the Key of C?
D
What is the Step Up in the Key of F?
G
9’s are my favorite Step Up because they often support the melody. In case you’re interested in the “why” behind chords, a 9 replaces 1 with 2, and tags on a 7. (2 + 7 = 9)
G9 – b, d, f, a
G9 usually comes after Dm.