This assumes Word XP (2002) or 2003. Word Vista (2007) probably has something similar.
1. Click in the paragraph.
2. Click on the Format->Styles and Formatting menu item.
3. In the bottom part of the sidebar that pops up, the style for your paragraph should have a bold box around it.
4. Hover the cursor over the style. A listbox arrow should appear. Click it.
5. Select Modify from the list box.
6. Click the Format button and select Paragraph.
7. In the Special list box in the Indentation section, select First Line.
8. OK out of everything.
All paragraphs in the document with that style should adjust themselves.
Now, if you want to carry this one step further and fix the style on the template your document is based on (probably Normal.dot, but not necessarily), do this:
1. Click the Tools->Organizer menu item.
2. In the left-hand list box, find and click on the style you changed.
3. Click the Copy button between the two list boxes.
4. Click OK.
When you close your document, you may see a warning message asking if you want to save the changes to Normal.dot. This is an anti-virus measure, intended to alert you that something has changed in Normal.dot. In this case, you made the change, so you want to accept it.
That should do it.