First of all, You have to make sure that the domain is more than 60 days old and is not locked by the current registrar. you also have to have the authentication code (EPP Key of the domain).
After that, client can initiate the transfer from domain name registration account, he will need to verify the domain's transfer using the email address registered with the domain. Then you just needs to wait for the process to be completed.
If there's problem during the process, you can contact us at http://services.iwebhosting.com.my