If the particle is on the layout of an outline just toggle the particle to disabled in the top right hand corner of the particle settings (changes from green to red). Or, you can disable the particle entirely (regardless of whether any instances are placed on a layout or not) by going to "particle defaults" tab of the base outline and again changing the toggle to disabled in top right of the particle (green to red).
All of that said, you still should not be adding any more particles to your template than you actually need. This is because regardless of whether the particle is used or not it's scss is still going to get compiled into the site and it's js still loaded too (still slowing your site down) - so my advice is don't do it.
Regards, Mark.
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