Migrate Categories

Hi guys, I’m in the process of merging two blogs together. I want to reshuffle the categories I am using. Is there an easy way to migrate all the posts from one category to another category?

For example:
I have 10 posts in the category ‘software’ and 5 posts in the category ‘hardware’. I want to move all of those posts into a new category called ‘technology’ on my blog.

The only way I can do this (for what I have seen) is to go into each individual post and remove the post from the old category and to add it to a new category. I have over 120 posts on both of these blogs so that is going to take quite some time and there is an increased chance that I could make a mistake.

I’m hoping there is a plugin or a simple way to select all posts from a category and to move them to another category. I haven’t found anything yet though. Any ideas?