For example i have a web site that have 5 well optimized sites and for thoes 5 sites i want to be ranked good. Every site is optimized only for one keyword so When somebody say add content to your site it means add content to the well optimized sites or just add content as a separated site.
Both ways will help the ranking of your website. On one hand you're adding new pages, expanding your site, building more links, and adding new content for spiders to crawl. On the other, you're adding more content to an existing page, but SE's will obviously give higher quality rank to say 2000 words of content as opposed to 500 words of content. As long as you're adding relevant fresh content to a website, it will improve. If you ONLY want those 5 pages that you've optimized to rank better, then add the fresh relevant content them to them.
But for example on my home page i can't add more and more content i need to delete some lines because it wont look good. Is this ok if i put article in monday and change after a day i delete the old and put new.
Sure, but make sure that there is still a way to access the article that you're removing from your homepage. You never want to get rid of any content so that it can't be found again. Perhaps have a snippet of the article on your homepage and have it link to the actual article page.
i agree with DSeguin...you wouldn't want to loose those content that you have given time before and it'll also give you some results...add fresh and unique contents to your site...