Update change all or a part only ?

Hi to all good morning,

Just wan to know if possible please, what's the best solution if you update a page

1- change only a part of the page
2- do not change just put more text
3- change all as soon as you can

Like i saw more i change exemple every 15 minuts new text i have tons of visits, if i put more text in old page, slow slow.

So what's the solution please. (make new as soon as you can)
like google race

what kind of page?

iframe change meta description or messages in phpbb forum,

the trouble is the same with google cache.

you can make 50 changes per day never update cache (the page has pagreank 0 and no backlinks).