i try to update my laptop. the KB2919355 update install 99% and its roll back it show undoing changes. my friend fix this problem in his PC by resize 100 mb active and boot partition to 700 mb .by using mini tool partition wizard . but cant merge that 100mb partition because it is fat32 format . Have any other solution to this issue?(i use dell inspriron 15 3000 series laptop) 

Hi pmadusara,

Have you got any error code or error messages?

Please check the update history for more information to troubleshoot this issue.
Control Panel\All Control Panel Items\Windows Update\View Update history
Here is a link for reference of troubleshooting:
Install the Windows 8.1 Update (KB 2919355)
http://windows.microsoft.com/en-us/windows-8/install-latest-update-windows-8-1

Best regards