Find a helper to hold the head of your mattress up. Place some books on the foundation underneath. Use as many books as is necessary to reach the desired height.
Use a helper to lift up the left top leg of your bed. Slide one or more boards under the leg until it's as high as you want it to be. Repeat this step with the right top leg of the bed.
Have a helper lift up the head of your mattress. Slide a mattress wedge underneath. Since wedges are available in different heights, widths and depths, you can buy one that will put you at the exact height you want.
Use a mattress lift to raise the top part of your bed up. A mattress lift is typically a rubber bladder that's positioned underneath the mattress. It's attached air pump is plugged into a nearby electrical outlet. You use the control to inflate/raise or deflate/lower the mattress.