recordset command to update 1 field

[Donna]

I have a database table that has one field that is constantly changing, based
on college class registration. This field keeps track of requests to
register for a class when the class is already filled. It helps the
department know if they need to add another class section. This field
changes constantly. The department would like to update this field 3-4 times
a week. How can I write a procedure that will just update this one field -
the primary key is two fields: "TERM" AND "CRN". This data is imported into
Excel from the school registration website and will imported into Access from
there.