Use SPOFS after the sprite has been initialized with SPSET.
SPOFS works using the coordinate grid instead of moving relative to where the sprite currently is, so use variables to dynamically move your sprite.
like this
SPSET 0,1
X=100:Y=100
@LOOP
STICK OUT TX,TY
X=X+TX*2:Y=Y-TY*2
BTN=BUTTON()
IF BTN AND 1 THEN Y=Y-2
IF BTN AND 2 THEN Y=Y+2
IF BTN AND 4 THEN X=X-2
IF BTN AND 8 THEN X=X+2
SPOFS 0,X,Y,0
WAIT 1:CLS
GOTO @LOOP
