add a class name to images

i have a website and i use juicyads for popunder
and every week google send me alerts for bad Abusive Experience
i contact with customer support and they told me

Sorry for the delayed reply. I had to hear back from our techs. To pop the ad on images only.... first you need to add a class name to your images. So something like the following...

<img src= "img/test.jpg" class="thumb"/>

Then you just need to update the list of tags that the Pops script looks at with the class name.

Example :
var juicy_tags = ['thumb'];

could any one help me with that?
i have no programing experience
i use wordpress and RetroTube theme

for HTML tags 'class' just works like a description. so non technical explanation to solve your problem is: " all your images that are also links; add a description for the ad it links to "
so there are two parts -- in your word press theme the <img> tag, you would add "class='promo_link'" in this case i made up the 'class' name called promo_link..i don't know what your juicy_tags really are.

-- part2 is the juicyads script has some reference you need to update with 'promo_link' so it will >apply< the code to the <img> tags

i don't really use this system so i am guessing based on the description you gave. good luck