how offten I must update my site

it all depends on what kind of site you are running...(this is just common sense)

 

Its good to add fresh content to your site but only if its a relevant addition, i wouldn’t do it purely for SEO purposes.

 

Once a week works fine

 

Agree. Once a week is good enough.

 

It depends on the site, niche, etc.
I like sites being updated daily. More pages in Google index means a lot more organic traffic.

 

Are you completly sure about this?
I have 20-120 search-engine-bots online at my forum all the time, and my site seems to be pretty low-ranked.
Thanks.

 

I had an old blog, with quite a good ranking, then i didn't posted much on it and fell down in ranking, even disappeared from the first page on google, then i just posted a few posts and got back again for the same keywords, so i think basically 1 time a week would be ideal update time.

 

It really depends on your site what what type of information you would like to update

 

Most importantly, the updated content should be unique and has high-quality.