Need to edit htaccess while moving on Wordpress

I am moving my site from another CMS to WordPress. I currently have this .htaccess

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /atoponwp/
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /atoponwp/index.php [L]
</IfModule>

# END WordPress

As I need to keep my old links in Google Search consistent with the new site, how can I modify current .htaccess in order to have the following rule accomplished?

Old links:

http://<mysite>/index.php?page=<pagename>

should be changed to:

http://<mysite>/<pagename>

Thanks for any help.

Fabio