You can lower it with a pH down.
Check out these links:
You can add sulfur to the soil with epsom salts, as @garrigan62 mentioned above, and this can help acidify your soil slightly and may help with some associated deficiencies. As well as some of the other sulfur additives mentioned in the links above, however I’m not fond of adding aluminum to my growing medium, and I personally would not use that one.
You can also use sulfuric acid, easily obtained at a autoparts store as a battery “refill”. This is pure sulfuric acid and has never come in contact with a lead acid battery’s lead, and so it does not contain any lead and can be mixed with purified water to make your own pH down, or you can easily buy the stuff from general hydroponics at places like amazon or even find it at many local specialty garden supply stores now-a-days.
Here is a kit with those drops and pH up and down mixes:
http://www.amazon.com/General-Hydroponics-GH1514-Control-Kit/dp/B000BNKWZY/?tag=greenrel-20
Check out this link as well about adjusting pH down:
~MacG