MySQL error code: 1175 during UPDATE in MySQL Workbench

I want to update the column `visited` to give it the value 1. I tried this command in the SQL editor inside MySQL workbench: UPDATE tablename SET columnname=1; But I get an error that says: > You are using safe update mode and you tried to update a table without > a WHERE that uses a KEY column To disable safe mode, toggle the option > .... I followed the instructions, and I unchecked the `safe update` option from the `Edit` menu then `Preferences` then `SQL Editor`. But I still get the same error. What is wrong? How can I update the value?