how i use update query same like select query

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C#

ASP.NET

comm.CommandText = "SELECT sponcorid from Registration_Master WHERE regCode='" + temp + "'AND count_mem=" + count_mem + "";
comm.CommandType = CommandType.Text;
comm.ExecuteNonQuery();

and i want to update sponcorid how i use it
here is update query..

comm.CommandText = "Update Registration_Master SET regCode='" + temp + "'AND count_mem=" + count_mem + "";

but what should i write in WHERE condition???
if sponcor is available for registration code(regCode) then sponcorid counter(count_mem) of that regCode should be updated