Is it possible to change the Port number....

Is it possible to change the port number 5222 to port 80 to make ejabberd to listen to the requests from port 80

There should be no problems, just replace 5222 with 80 on ejabberd.cfg. Or you can add a new entry in 'listen' section, similar to the 5222 or the 5223 ones but replacing the port number. Don't forget to specify the same port on the client.

I tried changing in ejabberd.cfg file, the server was able to start but I am unable to login from my exodus client.

Did you check the server logs? If I try to use port 80, Erlang says:

=ERROR REPORT==== 4-Jun-2005::20:44:42 ===
E(<0.236.0>:ejabberd_listener:80): Failed to open socket for {80,
         ejabberd_c2s,
         [{access,c2s},
          {shaper,
           c2s_shaper},
          starttls,
          {certfile,
           "/home/ejabberd/server.pem"}]}: eacces

Erlang failed to open socket on port 80 with error code 'eacces'. From the Erlang/OTP documentation:

eacces
    permission denied

I run ejabberd with a non-privileged system user, that has no permission to open a server in port 80. If I use port 1080 instead of 80, ejabberd starts correctly and I'm able to connect using 5222, 5223 and 1080.