On the text clip, click the FX icon. Then click the large green + at the top-left of the window and choose the SCALE effect.
With the red-line cursor at the head of the clip, create a keyframe by clicking the smaller green + sign.
Move the line to the place where you want the movement to end. Drag the right-bottom handle in the preview window, or use the sliders, to make the text as small as you like - or vanish.
Create another keyframe, if necessary. Keyframes are signified by tiny squares. Preview the result and make adjustments as needed.
For more info, click the ? at the top-right of VP's window. In the Effects and Transitions section you will see "Animating Video Effects."