Thanks Alex. Looking at it close I can see that is possible to move the lamp
up an down.

I'm certain that the I'm not getting even coverage, because slight moving the
lamp change the illumination in a sheet of white paper when I put the mask
without any film.

Any way to determine the correct position? On the side of the enlarger I have
this info: "Condenser lenses: double plano-convex 120ϕ 80R" (what the "120ϕ
80R" means?)