1. please close Diablo3 first, and use Notepad open "agent.db" this file (*1)
　
Where is the "agent.db" file? (*2)
Win7 & Vista is in C:\ProgramData\Battle.net\Agent\agent.db
WinXP is in C:\Documents and Settings\All Users\Application Data\Battle.net\Agent\agent.db
Mac user can see this post　(thanks NDT)
http://us.battle.net/d3/en/forum/topic/5152415037?page=5#100
　
**NOT the Diablo3 game folder's agent.db !!　(thanks Darkstaf and Eliarainne)
　
　
2. find ALL(there have three or more)
http://****.patch.battle.net:1119/patch and change to http://enUS.patch.battle.net:1119/patch
　
**** is your client version. (like below)
enGB
enSG
esES
deDE
frFR
itIT
plPL
zhTW
koKR
esMX
ptBR
　
　
3. don't forget save file!! then close Notepad and restart Diablo3, it will update to 1.0.2.9749
　
　
　
IMPORTANT
　
1. backup the agent.db to other folder before you modify it.　(thank Fight4Love)
　
2. If you can't see the file or folder, you can see the following microsoft web support.
　　　How to show hidden files
　　　　Winsows 7
　　　　　http://windows.microsoft.com/en-us/windows7/Show-hidden-files
　　　　Windows Vista
　　　　　http://windows.microsoft.com/en-us/windows-vista/Show-hidden-files
　　　　Windows XP
　　　　　http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/win_fcab_show_file_extensions.mspx
　
3. you can change it back, after you updated it. (please dont forget close Diablo3 before you change it!)

Source: Diablo 3 forum