Login to WordPress as admin, go to plugins. Install and activate Disable/Hide Comment URL plugin. Once you activate the plugin it will remove the website url field from the inbuilt WordPress comment form. This should help you to reduce spam comments. The number of spam comments we see are posted with the sole intention of getting back links. If the website url field is disabled then such spammers would not consider your blog for posting spam comments.
You might have approved comments in the past. Those comments must be having website url linked to the name (usually a keyword). If you want to keep the comments and remove the website url linked to the name (comment submitters name), install and activate the plugin Disable Comment Author Links. This plugin would strip the urls from all the approved comments. This plugin will not remove the url posted in comment area.
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