Sometimes you can't adjust the bed any higher. Apparently it is not uncommon for the bed to be so low that any attempt to raise the bed further causes the adjustment screws to pop off, causing the springs to push the bed up and hit the nozzle.
Administrator Samuel Pinches solved this problem as follows:
“Rather than raising the bed up higher, you can actually lower the position of the Z-endstop so that the nozzle will settle in a slightly lower position. Inside the right column is a small white block with a switch on it. The switch is attached to the white block with two small screws. The white block is attached to the frame of the printer with two larger screws. By undoing the two larger screws, you should be able to adjust the vertical home position of the nozzle, to allow you to be able to properly calibrate your bed.”
The bed won't go any higher The adjustment screws fall off I can't adjust the bed any higher The bed won't go any higher