MySQL Update Query not working and not updating records

I have a table

stu_id,stu_name,stu_age the first stu_id is auto increment column ..

1 nnnnnn 25

2 sssssss 23

3 vail       22

  Code:

OleDbCommand cmd = new OleDbCommand("update bannerdetails set bannername='" + textslidename.Text + "',bannerimage='" + upload.PostedFile.FileName + "',bannerlink='" + textslideurl.Text + "' where id=" + userid + "", conn);

now i want to update the ssssss for 4 ...if u anty idea pls give me..