I am writing a report and have to provide references for the same.
If I change the reference number how can I update it in entire document. If I have given reference number as  and if its updated to  how can I change it in entire document?
So cross-reference helps you to create a hyperlink that will take you to the another location in your document.
In MS Word you are allowed to create a cross-reference only to headings, footnotes, bookmarks, captions, and numbered paragraphs.
First let's use a simpler example and that's referencing text that is on a particular page.
To do that click on the text you want to reference and create a bookmark (Insert Cross-Reference, select "Bookmark" as the reference type and "Page number" under "Insert reference to".
One feature that I get questions about is the cross-reference capability.
This is the ability to insert text that references things like numbered paragraphs.
Tried with select all text and updating fields, but its not solving the purpose....
Sometimes you’ll add a cross-reference to a figure or table, and part of it (the number usually) will display in bold text.
Page number, it will insert page number in the document where you have the slected bookmark.
Paragraph number, it will insert the number of the paragraph where the bookmark exists and so on.
In case if you deleted any of the reference types to which you had created a cross-reference you have to update your cross-references.