how to upload only image ( jpg, bmp ) and size of the photo not more than 1MB ?

I have created upload button as per below and im able to upload the photo to upload folder in my web application .
But im not sure how to determine only can upload image format jpg & bmp and size of the photo not exceed 1 MB ?
Pls help . Below are my coding :-
FYI , my web developed in asp.net C# and mysql . Kindly let me knw if need more info . 
 
 protected void btnUpload_Click(object sender, EventArgs e)
        {
            if (FileUpload1.PostedFile != null)
            {
              
                Byte[] bytes = FileUpload1.FileBytes;
        &nb ...