You have that option in your control panel.

SpamAssassin uses a wide variety of local and network tests to identify spam signatures.

If you are using the cpanel and have cpanel login details, it is very easy to configure. You can check the following instruction to accessing the Spamassassin

1) Login to your CPanel

2)Go to the Mail Section

3) Click on Spamassassin

There you can easily configure the spam assassin.