First you need to Get row data from grid or from method and bind('show') this data in your textboxs, dont forget to save ID in variable or disabled textbox
public static Category Get(int id )
{
FaturaEntities ent = new FaturaEntities();
return ent.Categories.Where(x=>x.id==id).FirstOrDefault();
}
then to update you need this method
public static void Update(Category category)
{
using (var dbCtx = new FaturaEntities ())
{
dbCtx.Entry(category).State = System.Data.Entity.EntityState.Modified;
dbCtx.SaveChanges();
}
}