You cannot remove an IDENTITY specification once set.
To remove the entire column:
ALTER TABLE yourTable
DROP COLUMN yourCOlumn;
Information about ALTER TABLE here
If you need to keep the data, but remove the IDENTITY column, you will need to:
- Create a new column
- Transfer the data from the existing
IDENTITYcolumn to the new column - Drop the existing
IDENTITYcolumn. - Rename the new column to the original column name