I want to replace a specific part of a url, but only within a specific div, been trying with regex (yes I'm a regex newbie) but just cant wrap my head around how to get this to work and would appriciate any helping hand

I want to replace /images/ with a new folder /design/abtester/nyaproduktbilder/
Reason for this is that I want to run a sitewide A/B test with new product images

I have this part of code

```
<div class="visaprodbild"><a class="fancyBoxLink" rel="produktbilder" href="/images/BR501.jpg"><img class="hand" alt="" title="" src="/images/BR501.jpg" border="0" width="330px"></a></div>

```

Problem is that I cant just find and replace the /images/ part, cause there is a lot more other images on the page using /images/ and I cant move the original product images to a new folder. 

So I need to identify the /images/ part within the div above

Sorry if this was an unclear question for help, but just so lost I can hardly explain what I need to do.