you cannot just copy and paste, first you will need to unregister the cdo.dll then copy and paste and then register the new one.
locatae the cdo.dll to where it resides on the bes server
1.) To unregister cdo.dll in dos promt change root to location of file ie c:\programe files\Exchsrvr\bin>
Then type regsvr32 cdo.dll xxx8211;u
to unregister this file.
2.) then copy the new cdo.dll file in the same origanal place and register this by going in dos promt change root to location of file ie c:\programe files\Exchsrvr\bin>
then type regsvr32 cdo.dll .
however if everything is working fine i would leave it as the saying goes if its not broke dont try and fix it.