How do I set Grove GPS to use A-GPS?
A-GPS uses a network connection to download GPS almanac and ephemeris data to enable satellites to be located faster. Otherwise the GPS device has to wait for the data to be sent by a satellite, which may take up to 12.5 minutes. Alternatively, the GPS device can send noise GPS data to an assistance server which will process it and send back a fix.

A-GPS requires a network connection to an A-GPS server. You can't just 'turn it on'. There are some modules out there that combine GPS with a 3G modem which do A-GPS automatically.