Log into your PayPal account then click on  the settings (gear) icon.

Then click on Seller Tools in the in the secondary menu.

Next, find the section titled "PayPal buttons" and click Manage.

For the shopping cart system select the "Add to Cart" button.

Enter the relevant information for  your product.

Then click the "Create Button" button.

After creating the button, the next screen will generate the HTML button code. Copy this code and paste it into the editor of your website where you'd like the button to appear.

Pasting the code into the Content Editor

Button now visible on product page of website.

Log into your PayPal account then click on  Tools > All Tools. 

Next, find the section titled "PayPal buttons." 

At the top of the next page will be a link titled "View your saved buttons", this is where the list of products will be located.

Existing products are show in a list.
Click the product to edit then click "Edit button" from the "Action" menu on the right.

Edit the product then click "Save Changes" 

The button code will appear after saving. Copy and paste this code to replace an existing button or to add the button to a new page.