Yes. With an SQL statement you can update any field you want.
SQL Seminar Part 2 shows how to do this in detail.

Matt
First, I moved this to the Access Forum.  The AccessDev.NET forum is used to request a developer to help with a project (usually paid).
This forum is more appropriate for help questions.
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To your question - Yes, it is absolutely possible.  I see that you are up to Expert 1 (GREAT job! Keep going.)
I would caution you to not try and do to much to fast.  BUUUTTT.....

Go check out the Intro to VBA video.  That will give you a great starting point.  Put on your training wheels so to speak.
You wouldn't have a brand new driver jump right on the freeway - Right?

If you have already watched it - go watch again.  Start and stop as needed while doing what Richard is doing in the video.
That is the best way to cement it into your brain.  

BTW (hint) - the part in the Free video where you change the value in the FamilySize is very similar to what you asked.

The thing you are training your brain to do right now is look for similarity between what you need to do and what Richard is showing you.

There are lots (and lots and lots) of things to teach you. The best thing is start at the beginning (video above) and keep learning a little more each day.