Need redirecting old site to new site

[-sky-]

go to your old domain control panel use FORWARD option and place your new site URL

no need script use domain panel FORWARDING

[balak]

What you would need to do is add the Site A's domain on your VPS B and then do a htaccess redirect.

Options +FollowSymLinks
RewriteEngine on
RewriteRule (.*) http://www.SITEB.com/$1 [R=301,L]

Because if site A's domain is no longer hosted anyway (shutting down VPS A), the redirect would stop no matter which method you use so you have to ensure Site A is hosted some where.

this make sense, but is there any other way? so that i don't have to host site A anywhere.

[-sky-]

lol
this no need host just go to your old domain panel then look feature domain forwarding
place yout new domain URL