On a Linux server, /var/log/audit.d is taking up more than 40 GB space. The folder contains lot of files with name save.*

You can delete these files

root@server1 [/var/log/audit.d]# rm -f save.*

Now you may disable audit service. To do this, first stop audit service.

root@server1 [/var/log/audit.d]# service audit stop
Shutting down audit subsystem [ OK ]
root@server1 [/var/log/audit.d]#

Now we can disable the service

root@server1 [/var/log/audit.d]# chkconfig audit off

Or you may use graphical interface to services

root@server1 [/var/log/audit.d]# ntsysv

and remove the selection for audit service.