TTL is one of the fields on a DNS record, so it is edited there. You can usually find it in your hosting control panel under something like Domain Tools or DNS Zone Editor.
Remember that TTL is one of the data points governed by TTL. If you change the TTL for a domain name from 864000 (24 hours) to 300 (five minutes), hoping that it will speed up global DNS propagation, servers and routers won’t see the updated TTL until the check back for the entire DNS record. So, you might want to change the TTL a day or two before your change your IP address, if fast propagation is a high priority.
