With Filter set to Annotation, pick on the ref dim, RMB or right click >Proerties [or >Edit >Properties]. When the Properties Window appears, click on Move and pick on the new location. To move again, you have to click on Move again.
ceferinos thanks! ANNOTATION D%&$ ... another question along the same subject of ref dims, is there a config pro setting to control the text height other than text style? I have too many ref dims to change one by one.