Simple step. Just Follow this step.
1. go to https://www.google.com/adsense
2. login with your account
3. go to “Adsense Setup” and Click link “Adsense for Search”

5. follow step to get this

now, create new file “search.html”, use your favorite editor. i’m use vim …
write this:

and upload “searh.html” to your wordpress. Then your directory seem like this:
– root
—- wordpress folder
——wp-content
——bla bla
——search.html

now, edit your template.
find form search, “header.php” in my case.
Change “old form” like this:

and done.
Thanks for reading