Varchar to numeric

hi the result of this query is that the oldvalue and newvalue are varchar255. How can I change the select so the old and new values are numeric?

SELECT TOP (100) PERCENT BCM.Datum AS Date, BCM.FieldName, SI.ItemCode, SI.[Item Description] AS ItemDescription, BCM.OldValue, BCM.NewValue, BCM.FullName AS Modifier, SI.Status
FROM dbo.GRV_Audit_BusinessComponentsMutations AS BCM LEFT OUTER JOIN
dbo.GRV_SalesItems AS SI ON SI.ItemCode = BCM.Datakey
WHERE (BCM.FieldName = 'CostPriceStandard') AND (YEAR(BCM.Datum) = 2020)
ORDER BY Date DESC

SELECTTOP(100)PERCENTBCM.DatumASDate,BCM.FieldName,SI.ItemCode,SI.[ItemDescription]ASItemDescription,BCM.OldValue,BCM.NewValue,BCM.FullNameASModifier,SI.StatusFROMdbo.GRV_Audit_BusinessComponentsMutationsASBCMLEFTOUTERJOINdbo.GRV_SalesItemsASSIONSI....