You should be able to set the canvas size and scale. If you have problems, try to use the wheel mouse or press right mouse button to enter the value manually.
Viewing post in Possible to scale up an export?
Hey thanks for the reply, though that's what i was trying. If i set the Scale value to "2", which gives me an output of 128x128. The problem with that is the pixels in the animation would be too small for the rest of my art work. What i've done primarily is for example draw a 32x32 sprite, and then i export it at 200%. So it looks the same, and has the same number of "pixels" in the artwork, but is a 64x64.