See "Changing the I2C address" at the bottom of the tutorial page: http://learn.adafruit.com/i2c-spi-lcd-b ... ect-to-i2c
The A1, A2, A3 address pads referred to in the tutorial are on the lower left of the board.
What is the limiting number of Lcds that can be supported - the tutorial says 7 - but where does this limit of 7 come from?
The chip supports 3 bits of addressing. I haven't tested it, but I believe you can actually have up to 8, since 3 bits of addressing allow for addresses from 0 to 7.