Wordpress/need to change header&footer GOOGLE BANNER CODE, direct me through

General information for the website: basic wordpress
Description of requirements/features: this is a basic job for someone who has done it before. i nearly did it but banner appeared in the wrong place. i want to edit change google banners header and footer codes. when i open these links in edits, from the appearance page i see the php pages and open them but am confused to know what part to delete and what part not to. i have the new codes that i would like to implant. i tried with the header one but another banner was added and old one stayed so i but it right from where i started again. with the footer one i could not even work out where the code was. i would like to save the pages on note pad and email to you and send you the new codes so you can see and you highlight tell me what parts i have to remove from the pages im trying to edit and where new codes need to go. google offer codes in two formats. i fix it, try it, if it works i let you know, if not you have to see what is wrong. that so that i can continue to put it right. we will do one page at a time, the header one first followed by the footer one.
Specific technologies required: google adsense, wordpress, php
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