updating theme over existing theme/site

[pm_wrus]

I have an existing magento 1.7.0.2 site and I want to update the theme so its responsive. I cant seem to find any tutorials on this specific topic, unbelieveably. Assuming its not just as easy as installing a new theme and then activating it in the magento panel.

Im mostly a front end developer/graphic designer but I do have a decent grasp of where and what stuff is but Im certainly a novice still. Ive only worked on existing magento sites, never started one from scratch or updated the themes.

TIA

[John Sim]

Have you read the official documentation already:

http://info2.magento.com/rs/magentoenterprise/images/MagentoDesignGuide.pdf

Also, here's another resource that comes in handy. In case you wish to add JS & CSS files in custom locations:

http://store.redstage.com/blog/2012/07/24/how-to-properly-include-custom-css-and-js-files-in-magento...

[pm_wrus]

What Im trying to find out is whether there is an "easy" way to merge a new theme with an old theme without hitting every part of the site to adjust things after I switch over. From what Ive found out ( and it makes sense ) is there is not an easy way and you will end up retweaking the site to fit the new theme ... or am I searching poorly?