HI Reddy,
if you use the KYF , fisrt check where you use this KYF. Then delete the data from these objects where your KYF is used. And tfinnaly change its type.
And yes you cna do a complete deletion, you can delte only selected requests and you can also do selective deletion! Note that delete a single request and slective delitions especially when you have a lot of records takes time...
BR,Todor