Changes does not accept in c# at runtime

Question

hi,

   I am doing one c# windows application project. The project is well going but i have one big difficulties i.e. when any modification done in form and coding , the modification is does not accept while runtime, (before modification form and coding is running).Example: i have one form Name:monthReport while clicking a button  the monthreport will run, i delete the monthreport form and generate a new form Employeemonthreport. During runtime my old form i.e monthreport is calling it does not accept employeemonthreport and also any changes done in any form does not accept during runtime. 

Pls help me very urgent......

Thankz in advance to everyone.....