updete Amount Column??

Question

 

hello

i want to update Amount Column in Table that have 1000 and i add 1000 agin  add value then update vale is 2000 are written i table colum 

what can i do 

 

 

 

upQuery = "UPDATE FeeDeposit SET Amount ='" + textBox1.Text + "'WHERE Admission_ID=" + labstuid.Text;

SqlCommand cmd = new SqlCommand(upQuery,con);

cmd.ExecuteNonQuery();

con.Close();