Installing the pixel in WordPress is very easy. There are multiple ways of doing it, you can use a free plugin such as the Header and Footer scripts or you can modify the files of your theme which is not very advisable especially if you don’t really know what you’re doing and also to prevent the loss of the pixel when you update the theme.
If you use a plugin that inserts custom scripts on your WordPress be sure you paste the Pixel code on the header of your site between the <head></head> tags, not in the footer.
Another possibility (depending on your theme) is to use your theme’s settings panel (if your theme has one) and insert the pixel code on the Custom JS or Head Scripts section. Not all themes have this option so you might want to use the plugin option instead as depicted in the image below.