Renaming an index replaces the current index name with the new name that you provide. The specified name must be unique within the table or view. For example, two tables can have an index named XPK_1, but the same table cannot have two indexes named XPK_1. You cannot create an index with the same name as an existing disabled index. Renaming an index does not cause the index to be rebuilt.
When you create a PRIMARY KEY or UNIQUE constraint on a table, an index with the same name as the constraint is automatically created for the table. Because index names must be unique within the table, you cannot create or rename an index to have the same name as an existing PRIMARY KEY or UNIQUE constraint on the table.
To rename an index
The following example renames the index IX_ProductVendor_VendorID in the ProductVendor table to IX_VendorID.
EXEC sp_rename N'Purchasing.ProductVendor.IX_ProductVendor_VendorID', N'IX_VendorID', N'INDEX';