Exchange Server (MB Role) not detecting exchange updates after re-install

Hi 

We had some application issues with exchange server 2010 with SP1, it has a mailbox role installed.due to this issue we formatted C drive alone and re-installed windows 2008 R2 (SP1) + exchange 2010 (SP1).

Server detecting OS updates but not exchange updates. i need to install updates rollup for exchange server.

Please guide me 

 Thanks

Senthilkumar