Hello Ambarish,
You would need to use the TREX admin tool for deleting and creating the index. Please go through below links and also pay attention to the use case.
Deleting an Index - Search and Classification TREX - SAP Library
http://help.sap.com/saphelp_erp60_sp/helpdata/en/46/cdfde54464270be10000000a11466f/content.htm
I would also like to know the reason behind trying to deleting the index.
Thanks.
Best Regards,
Anita