Access question -- replacing data in a field with another

Question

I have a table in Access that contains vehicle information from a dealer.
There is a stock # field and a photo URL field. The image title should match the stock #. Is there a way to make the two fields match?
Here is an example:

Stock #
10M020

URL:
http://myurl/image/12345.jpg

URL SHOULD BE:
http://myurl/image/10M020.jpg