how do I close the port 37 ?

I found this website: http://www.auditmypc.com/port/udp-port-37.asp
This website states that port 37 is used for:
"Time. Provides remote timing stat's of internal processing events. Security Concerns: Gives remote attacker info on host's internal processing load. Can identify critical processing times, plus output can be looped to echo port (7) and create a DOS threat to the subnet. Disable this port on all hosts."
Well I don't agree that this is a major security concern however it still might be a good idea to close it.

Okay since I don't have slackware I will relate to the general task of closing an unneeded open port.
First you determine which application is bound to this port. Run this: netstat --inet -anp
This will dump a list of all open ports along with the PID of their associated process. Then, once you have the PID you can determine which program it is by running: ps -ef
Once you've found the program simply stop it and remove it from your /etc/rc#.d folder so it doesn't execute on startup.
An alternative approach is to simply use the linux built-in firewall (iptables) to block access to unneccessary ports.
You may check this page for an iptables guide: http://iptables-tutorial.frozentux.net/iptables-tutorial.html

After changing /etc/inetd.conf, send SIGHUP to the inetd process to have them take effect:

killall -HUP inetd

omg you're right, I forgot to relate to inetd... killing inetd isn't a good idea.
if inetd is indeed the process that listens on port 37 you should definitely do what duncan_roe has suggested.

Sorry my delay.
Thanks.