how to open windows form in button click

Question

dear friends/sir

 

i want to open windows form c# . after button click

 

 in which i have only and only one form1 and button1

i have done this. now i want to button act like

if first time i pressed it it should show form1

in second click form 1 should be close and new form1 display.

 

my mean is to i don't want dublicate form.   

i want second time when i pressed button it should  load_form1() 

 

currently what happening when i'm pressing button more then 1time it creating

many instance of that form