Hi thanks Ryk,
I have changed it to KGs,
to change it u need to modify these files:

/admin/includes/languages/english.php
Line #570 : define('TEXT_PRODUCT_WEIGHT_UNIT','lbs');

/includes/languages/english.php
Line #376 : define('TEXT_PRODUCT_WEIGHT_UNIT','lbs');
Line #379 : define('TEXT_SHIPPING_WEIGHT','lbs');

/includes/languages/english/modules/shipping/zones.php
Line #25 : define('MODULE_SHIPPING_ZONES_TEXT_UNITS', 'lb(s)');


Thanks for the Help