How to improve upload/download attachment using OWA

Currently my company is using Exchange Server 2003 with OWA. The server is located in a country called Malaysia. My users from China are complaining that they are having problem uploading attachment when sending email using OWA. The uploading take a long time to upload until it timeout, hence upload failed. Is there any way I can improve OWA from Exchange server so user can upload/download without having any timeout issue?