Reactivation of Power Store needed (www.ozkat.com)

Thanks again for looking into this web site, there has been a purchase between your last message and this replay to you and the shipping and taxes came through in the final charges with PayPal (as a result of a successful sale containing all expected details we are in the process of fixing the weight in all products currently online). I have investigated the lack of weights in the products with the client and we decided to give a refurbish to the entire site, clean up the debris and reset the products from scratch (currently there are more of 2500 items stored in the products table). The intent is to setup a responsive site and by the look the upgrades on offer have responsive design as an option. The site was build with a 4.5.0 version (I think!) and the upgrade is a 4.5.4; I guess that the upgrade will carry the responsive templates, themes, CSS etc. I expect I will stumble into some hiccups and maybe something will confuse me in the process; I was looking from some tutorials on Web Assist but I couldn't find any. I hope you will able to offer some assistance (if I need to) while I will make the transition from one version to the other and if there is a potential need to make further customization by hard coding.
Over the years of my affiliation with Web Assist (10 years & plus) I have gained a great deal of understanding in php scripts, however I'm still miles away from been full of confidence in writing codes from scratch.
Thanks again for all your support.