"One of the dafault(ROM Code: A00), but i would like to select the other one (ROM Code:A02) How can I change it?"

Peter,
you can't change it within one HD44780U driver.
If you like to have European standard font (A02) it is necessary to order dispaly included right driver. See order information for HD44780U. A00 code means Japanese standard font.
Generally. We have problem to order A02's displays especially for less quantity.
"What does it mean this ROM Code..?"
You have 240 fixed characters in CGRAM (character generator RAM) and you can set up to 8 own characters in this CGRAM.
Use them in DDRAM.

Regards,
Vaclav