First go to the top of page 7 where you want to start the page numbering.
On Page Layout - open the "Page setup" dialog by clicking the small arrow at the bottom right of the "Page Layout" ribbon area.
At the bottom, select Apply to: "This point forward". Click OK.
This will put a section break at this page.
Note that adding a "Next page" break the normal way from the Breaks menu in the "Page Layout" tab will also do this for you, but that method would also add a new blank page. This would be the way to do it if you are in the process of starting a new page where you need to reset the page numbering. The method I have described above in this answer, is if you need to set a page section break in an existing document layout without adding a new page.
Then open the header or footer section for editing (depending on where you want the page numbers). You can do that by double-click the header or footer area on the page.
Turn off "Link to Previous" to make the headers different in this new section than the headers on the previous section.
Insert a page number in the header or footer (any form you like).
Then run "Format page numbers..." to open the "Page Number Format" dialog:
At the bottom, select "Start at: 1". Click OK.
Then you will see that the page number starts at 1 on actual page 7.
Reference to MS Office documentation with updated screen shots for latest version:
Start page numbering later in your document