can any one help me to reduce site loading time

Alain,
Mais Oui! Of course you will run out if memory if you use a cacheing system – Isn’t a cached page is a static copy of a page? – each time you modify the page it creates a new cached page. Eventually, even on hosting packages with” unlimited” space you will exceed the data storage on a shared hosting package and your account will be suspended – how do I know? It happened to me in 2006 and I lost a business through it.

Every time a user creates or modifies a page or post it creates a new cached item.

You end up with lots of copies of the same thing as well as all the revisions that wordpress itself keeps.

You can of course find all sorts of solutions that you can “plug in” thus adding to your already bloated site and further clog up the database with more useless rubbish.

One Classic way of speeding up your load times is to create a sub-domain for images – direct WP to draw the images from the sub-domain. Or even use a different domain – beware of hotlink protection though.
Voila!

If you need help on this subject then the Codex is a good place to start, also
https://yoast.com/

Is THE place for tips on SEO and wordpress optimisation.

General running of the site requires an in depth understanding of your control panel and its abilities – it is your friend