you can drop the compression just by buying different pistons
but i have found the best way to go is to buy forged pistons,
keeping the standard compression.
you will be able to run more boost with lower compression
but you dont always gain from this i.e.
standard compression with 10 psi =150 bhp
lower compression with 10 psi =130 bhp
these figures are not true but just an example.
forged items will be stronger, allowing you to run
more boost anyway