First of all as pikitsan said above .rar files are not installed in the
k810 phone, so you need to extract files first, by using WinRar (search in google for this software to download and install at your pc). then if you want to change your menu in
K810 then you need software Xs++ which is also downloadable from this site. go to download section and find it. you will also need a guide to follow the steps to change your phone menus. search for this too at this forum. no jar or no other way to directly change your menus in
k810 but hacking/cracking to your phone software(brain). Xs++ will do it for you. I changed my icons and i am happy with the new looks.
I hope you understand and will find xs++ and tutorial to do this.