WPDB update row with != in where clause

I'm using wpdb to develop a plugin to add a custom form to wordpress. To update a row, I use an array and wpdb->update(). WP Class Reference says:

My SQL code should be something like UPDATE ROW .... WHERE a='a' AND b!='c'. The problem is that != doesn't seem to be working, in fact from WP Class Reference: http://ift.tt/1khY1nN A named array of WHERE clauses (in column => value pairs).

I need to connect to an external database and fetch data from that database so I can't use any of the available plugins.