係好easy jar .
1) 擰大門lock個十字screw out ;
2) put half key into the old lock ;
3) use the key to 擰 the old lock out ;
4) put half key into the new lock;
5) use the key to 擰 the new lock in;
6) 擰大門lock個十字screw in ;
that's all .
if u only buy the "key膽" i buy $150 in mongkok. It's easy to change! Pls follow the Stephen's instruction! Any inquirylet me know. I only change by myself.