Possible to rearrange Headings in Style?

[ShaunBlake]

Problem: I need to change all instances of Heading 3 to Heading 4, and Heading 2 to Heading 3. I failed to discern the significance of text that should be elevated to Heading 2

Situation:

I just realized I've made a really foolish mistake about 20% into a ~2000 page project: I jumped into converting an ancient book into a PDF using Word as my editor before identifying some major divisions in the manuscript. They are subtle but significant to the cohesive message so it's necessary to correct it. 

I'm using Word 2007, and am fairly competent though admittedly not even a power user. I am reluctant to re-do the 600 pages I've processed, but know of no way to rearrange the headings without some kind of magic surgery to Styles.

Any advice will be appreciated (including lessons/tongue-lashes in impetuous behavior). TIA

[#2]

@ShaunBlake 

You can use Find & Replace for this. You'd have to start with replacing Heading 3 with Heading 4. Then replace Heading 2 with Heading 3.

In the Find and Replace dialog box (Ctrl+H), click the More button (if necessary) so that you can see all options.

In the dialog box, click in the "Find what" box and then click Format > Style and specify the style to search for. Similarly, click in the "Replace with" box and then use Format > Style to specify the replacement style. 

[#3]

@Stefan_Blom 

Thank you for taking the time to help me. I stumbled on your suggestion in another thread which didn't show up in my initial searches. Your approach of using Replace is better than the way I thought I would have to use, finding the headings and manually changing them in Styles.

That being said, I was _really_ hoping to find a way to access the attributes and change them externally—perhaps with a PowerShell script. My mess is spread over 30 files. I've never heard of manipulating MS Word documents that way, but the task is daunting so I wanted to reach out to the gurus and wizards before going very far on the repairs.

Kudos to you, your comments are great, and always courteous, even when helping a dunce!