Updated content is good for your site, yes? I am just wondering, if I update my content and have to re-upload/republish my pages each time, will I lose SERP's because it is like a new page? Or will the rankings get better even though I have to republish the page?
Only change content for "visitors", not just for search engines. Some of the highest Pagerank valued web pages contain the same content always. However, domain roots tend to have the highest since most backlinks point to them. Instead of changing a current web page, make a new one and follow proper internal linking structuring to allow spiders to find it easier.