Do you mean change a version 1 TK-880 to a version 2 type? I don't know if that in fact is possible. I've never tried it so if someone can prove me wrong, go for it.
Kenwood specifically states the firmware for a version 1 radio cannot be loaded into a version 2 radio, but lacks a warning on the version 2 firmware about what radio it can be flashed to. I would still be hesitant to cross-pollinate a type 1 to type 2.
Anyway, to answer your question, you'll need a copy of the firmware .hex file, a KPG-46 (or KPG-4) program cable and a copy of FPRO firmware upload utility. You put the radio into firmware program by holding down the "S" button as you power up. Then you browse the the firmware file in FPRO so the correct one is listed, connect the program cable and click "write". When it is all said and done the radio will generate a checksum and show it on the display. If it matches the one for the firmware file, you're golden.
Now getting the program cable is easy and any version of software includes the FPRO.exe program. The hard part is locating the latest firmware file. It is not something you find just floating out there. The only place I can think of that would legitimately have it would be a Kenwood dealer and whether they give it to you is up to them (check Kenwoods licensing on firmware). If you are going to go that distance just pay the bux and have them do it.