Anyway, I started to remove old and irrelevant NAT settings that were associated with my old dialer ,but when I've tried to configure the new NAT settings I got an error:
%Dynamic mapping in use, cannot change
After scratching my head for awhile I found the solution.
To remove old NAT settings on Cisco router you need to
1)Clear all old NAT translations
router#clear ip nat translatiom *
2)Disable old NAT pool settings
router(config)#no ip nat pool public_access 184.108.40.206 netmask 255.255.255.252
3)And finally, disable the translation:
router(config)#no ip nat inside source list 1 pool public_access overload
From this point you can safely configure the new NAT settings.