At the moment the paypal instructions are located at https://www.paypal.com/us/smarthelp/article/how-do-i-request-api-signature-or-certificate-credentials-faq3196. An important word of warning is Paypal seems to be always changing their interface and never for everyone at the same time. Those instructions as well as my screenshots below may not be accurate.
After logging into your PayPal account, click on your account name in the right hand corner. Choose account settings. 
Then choose API Access (at the moment it's the second link in the right hand column).
Choose this option:
You will have to validate your account at this point:
The resulting screen hides the information you need. Hit show the three times to see the actual codes. You may well be able to easily copy this section and grab all three but I know in the past I had to copy one line separately. Best to keep this info just in case you need it again even though you can access again at any time. 
