I believe you can't turn them off entirely, but here is what Facebook recommends:
Why am I seeing banner ads all over my timeline and News Feed? How do I remove these ads?
Some programs claim that they can give you special features on Facebook like seeing who viewed your timeline or picking out your own timeline theme. Most of these features don't exist, and these programs require you to download software that can cover your timeline with ads, make your pages load slowly and compromise your security.
Facebook ads don't appear as banners in the center, top or left sidebar of Facebook pages. If you're seeing banner ads in these locations, or ads that flash or play sound automatically, you probably have adware. To remove it, review the add-ons or toolbars that you've enabled for your browser and disable any plugin that promises special browsing abilities (like timeline themes or seeing who's viewing your timeline).
And here is another answer from Facebook:
Can I block Facebook Ads or opt out of ads showing on my account?
If you don't want to see a specific ad, you can click the x on the top right corner of the ad and choose hide. This will ensure that you no longer see this ad.
You can't block Facebook ads entirely. Ads help keep Facebook free and we strive to only show ads that are relevant and interesting to you.
Besides, to minimize ad targeting, you can go to
1. Settings > Ads > Ads and Friends > Edit > Pair my social actions with ads for > Choose "No one " and click "Save changes"
2. Settings > Apps > Instant personalization > Edit > and tick off "Enable instant personalization on partner websites"