I'm in my final edits for Dissertation corrections, and large part of errors are coming from formatting issues in the Table of Content. Here's few methods I find useful while working on my edits. I'm using Office 2013, so the required menu items might be different from your version.
How to change the Upper Case Roman Numerals to Lower Case?
This is due to your Table of Content (TOC) level 1 font is in All Caps. Press Ctrl + Shift + S to open the Apply Style dialog and select TOC1 and press modify. Go to format dropdown list in the bottom and Font, remove the check mark on the All Caps. This will change your Upper Case Roman Numerals in the TOC to lower case. If it is different, then check your actual page numbers whether they are in lower case.