known_hosts file

["jeff allen" <merc73jeff hotmail com>]

I have just recently updated the disk image on all 22 linux machines in our 
office. If I try to ssh into these machines I get the following error:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
48:d8:23:48:f1:f5:d4:41:df:70:d8:34:0a:8b:96:e9.
Please contact your system administrator.
Add correct host key in /.ssh/known_hosts to get rid of this message.
Offending key in /.ssh/known_hosts:20
RSA host key for frost has changed and you have requested strict checking.
Host key verification failed.

How does one go about updating the host key?

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