This tells you that the character definitions are stored in an array called font.
You need to look at what the bit patterns in there are and then create the new bit pattern (reversed and upside down) either on the fly when you need to display or as a new font table.
The normal LCD libraries allow you to have text going right to left instead of the normal left to right. Combine the two and you should have what you need.
An alternative is to just mount the LCD display upside down :-)