There are many number of reason you may want to delete you Facebook Account, but if you search in your Facebook Account settings you will not find a delete account button there, yes by default there is no option deleting your Facebook account, only you can deactivate your account.
But here is the official link which helps you to delete your account permanently:
Before you are going to do that, better try deactivating your account rather than deleting, because some days or months after if you want your account back you can do that by logging in to your Facebook account and activate it easily.
Deactivating Facebook account is similar to Deleting an account, no friends or followers can see your account,
Steps to deactivating Facebook account:
1. Click the gear button at the top right corner on Facebook, you will see the below drop down, click settings in that.
2. Then, click the “Security” link and you can see the link “Deactive your account” (marked in the below screen shot):
Follow the procedure to deactivate your account.