Hello Paul.
Thanks for you help on this , I was able to successfully upgrade php 5 on my windows plesk server and I found it very easy .
1) I downloaded the required php binaries , stopped plesk services , went to the path Program Files\Parallels\Plesk\Additional\PleskPHP5 ,
renamed the folder PleskPHP5 to oldPleskPHP5 , created a new folder
PleskPHP5 and extracted the binaries in it . Copied the php.ini from oldPleskPHP5 and placed in new folder new folder PleskPHP5 .
Thats it . Went to server option in plesk and refreshed components Management :bouncy: