Assuming that the numbers are being stored in text fields, and you're using
Access 2000 or higher, you can write a query that uses the Replace function
to correct your numbers:

MyNewField: Replace([MyOriginalField], " ", "")

Note that older versions of Access 2000 (i.e.: ones that haven't had all of
the service packs installed) may have problems using the Replace function in
a query. To get around that, write your own function that calls the Replace
function:

Function MyReplace(OriginalString As Variant, ChangeFrom As String, ChangeTo
As String) As Variant

  MyReplace = Replace(OriginalString, ChangeFrom, ChangeTo)

End Functioni

If you're using Access 97 or earlier, you'll have to write your own code to
mimic the Replace function. There's one approach in
http://www.mvps.org/access/strings/str0004.htm at "The Access Web"