There are several ways to do this.
One is by using an Update Query.
Add each field you'd like to update in query design.
In the "Update To:" row for each field:
StrConv([FieldName], 3)
Where:
[FieldName] = The name of the field you wish to update.
(3 = vbProperCase)
I'd certainly test this on a copy of the database first, to be sure it's doing exactly what you want it to do.
If it's extraordinarily large, I'd copy just one table or a portion of a table and paste it into a new test table and test your update on this test data.
You may also accomplish what you want with RecordSets. If you are not fluent enough, an Update Query would be best, I suppose.
Some caveats:
vbProperCase changes every word to proper casing (first letter uppercase, the rest lowercase). This may not be exactly what you want. Also, the strConv Function is for text fields. I don't know how it will affect other data types, without testing.
Shep
Edit:
I tested this with Text, Number (Long Integer), Date, Memo, Currency and Autonumber fields.
The function handles Text and Memo fields as you might expect.
It seems to (thankfully) ignore all of the rest with the exception of an Autonumber field, which it of course balks on. Autonumber fields are not updateable.