D to Asus4
How to transition from a D chord to the Asus4 chord.
The D → Asus4 transition is the same I → Vsus4 move in the key of D or any key where you're playing D shapes.
Chord shapes
Play the D chord in a D shape, and transition to Asus4 played in an A shape. Keep your third finger in the same spot and reposition your first and second fingers.
DFull
Asus4Full
Anchor fingers: finger 3 on B string (fret 3)