Малка поправка , забравих за маркирането на обработените записи. Ето ти поправената процедура

Sub UpdateDostavka()
Dim DB As Database
Dim R As Recordset
Dim RUp As Recordset

Set DB = CurrentDb
Set R = DB.OpenRecordset("Select * From Dostavka Where Mark = False ")

Do Until R.EOF
Set RUp = DB.OpenRecordset("SELECT [skladova nalichnost].KatalojenNomer, [skladova nalichnost].Broj " & _
" FROM [skladova nalichnost] WHERE [skladova nalichnost].KatalojenNomer= '" & R!KatalojenNomer & "';")
If RUp.RecordCount > 0 Then
RUp.Edit
RUp!Broj = RUp!Broj + R!Broj
RUp.Update
RUp.Close
Else
RUp.AddNew
RUp!KatalojenNomer = R!KatalojenNomer
RUp!Broj = R!Broj
RUp.Update
RUp.Close

End If
R.Edit
R!mark = True
R.Update
R.MoveNext
Loop

R.Close

End Sub