Dear Cristian,
Thank you very much for your prompt reply..!
1) I am now backing up (downloading all files) from the website first and then will update to WordPress version 3.1.2... May be a stupid thought, but I hope that updating will not effect any previous things on website?
2) I have also enabled "Deactivation Safeguards" as you mentioned.. and when I pressed "Save Changes", I saw a Note at the top of screen, that is below:
NOTE: s2Member security restrictions will NOT be enforced until you've configured a Membership Options Page. See: s2Member -> General Options -> Membership Options Page.
Again I hope that this enabled "Deactivation Safeguards" option won't affect on any of earlier settings too

S2Member levels will remain intact... Subscribers are not capable to enter the member's area..
Thanks for your help and support, I really appreciate it..
Reply me at your convenience, Thanks...
Mohsin