What is the best upgrade I can do on my SE K800i to get the most out of it?

[SeaMonkey]

Can someone help me please? How do I upgrade to K810?

First of all,let XS++3.1 Darwin to upgrade your CID49 to CID52,because than you can do what ever you want and next thing you can update your firmware with this tutorial XS++ 3.1 Guide-Flashing, Customizing, Recovering - Top Sony Forums and another thing - whan you first time connect your phone with XS(in Xs folder you find log) post log here without IMEI number and don't try to update with SEUS,because you get CID53