See the solder jumpers labeled A0, A1, A2 on your backpack?
Those are the A0, A1, A2 pins on the PCF8574 chip.
That is how you set the lower 3 bits of the i2c address for the chip.
http://www.nxp.com/documents/data_sheet/PCF8574.pdf
If you put a solder blob across the vertical pads it will alter the i2c address.
Then there are 3 address bits using A0, A1, and A2 that set the lower 3 bits of the i2c address
which you can set to allow up to 8 chips to be addressed on the same i2c bus.
If you have an i2c address of 0x27, then
more than likely the chip has a base address of 0x20 and
the three 10k resistors you see along the bottom of the board marked 103
are pullups on the A1,A1, and A2 pins which sets them all to 1
which sets the final address of the chip to 0x27.
To change the address, all you need to do is put some solder
(a blob that bridges the upper and lower pads)
on one or more of the A0, A1, A2 solder jumpers.
This will allow you to select an i2c address between 0x20 to 0x27
example, a solder blob on A0 would change the address from 0x27 to 0x26
a solder blob on A1 would change the address from 0x27 to 0x25
a solder blob on A2 would change the address from 0x27 to 0x23
a solder blob on all of them would change the address from 0x27 to 0x20
etc...
--- bill