Some email programs/servers/webmail have the ability to report spam.
If your’s doesn’t you could view the headers, find the IP the spam was sent from, look up the IP address, find out who to report it to, send them an email reporting the spam asking them to take action to stop it. If you do this be nice. It’s often a compromised mailbox/server/website or someone that fraudulently bought a service for the purpose of spamming.
The easiest way is to use SPAMCOP and it’s free.