Dim db As Database
Dim tdf As TableDef
Dim fld As Field
Set db = CurrentDb
Set tdf = db.TableDefs("tblTable")
'Is Auto an AutoIncrement field?
If (tdf.Fields("Auto").Attributes And dbAutoIncrField) = dbAutoIncrField Then
'You cannot delete a field that is used in an index.
'Let us assume that Auto is used as a PrimaryKey
tdf.Indexes.Delete "PrimaryKey"
'Delete field
tdf.Fields.Delete "Auto"
tdf.Fields.Refresh
'New AutoIncrement
Set fld = tdf.CreateField("NewAuto", dbLong)
fld.Attributes = fld.Attributes Or dbAutoIncrField
With tdf.Fields
.Append fld
.Refresh
End With
End If