Remove the handlebar by removing the four screws on the front of the stem and let the stem gently rest on your front tire (if it will reach, otherwise it will hang). Then take the stem apart like you did to take out the spacers. Take the stem itself and turn it over so the top is now the bottom. Put the stem back on the bike as you did before. Reattach the handlebar.You should now have a "negative" angle to your stem. A way to tell if it is at a positive angle before taking it apart is to use a straight edge (ruler) and line it up with stem where it attaches to the bike. Extend the ruler length towards the handlebar and if the stem rises above the ruler it has a positive rise and you should flip it over. If it falls below the rulers edge you have a negative rise and should leave it. If it's easier to tell after you take it apart just rest the part of the stem that attaches to the bike on a flat surface. It's pretty easy to see the angle that way.
Hope this helps. Happy riding.