now google mostly working on website content to give value more, so can you please tell me how long one content should be on website live and after how long we should replace old content with new content?
Google does like to see regular, fresh content. But it's not so much a case of "replacing" content as adding new content. So news items, blog entries etc. I don't see the point of continually updating an About page, for example ... but I'm happy to be set straight on that.
Add new content when you've got something useful to add. Replace existing content when it is out-of-date or when you think you can do something better. There is no fixed timescale, and Google won't judge you according to whether you update your site after a certain period of time.
I think evergreen content definitely has its place, but as ralp.m mentioned Google does indeed try to push the "fresh content" thing quite a bit as well. I recommend you post new content 2 to 4 times a week, but don't remove any old content as that can hurt your sites ranking drastically from keywords, links, etc... lost. I also recommend generating a xml sitemap that lays everything out and indicates how often certain content should be crawled. Wordpress has nice plugins that can generate them or you can manually make one.
Google loves to crawl sites with unique and fresh content and as we all know, a good content strategy is important for a website to succeed. So try to publish consistently.
Google crawl is not frequent as we think so according to me no need to worry too much and give new content with too frequent. But set time interval (blog post 15 days, webpage 3 months) to update, so that its easier for us to update with fresh and unique contents.
google always love to see fresh content, so you can change your site content but if you want to crawl your site very frequently then add a blog and write at least thrice a week