If the content isn't good then get rid of it and put something better up there! There's no advantage to leaving bad content on your website if you can improve it. What you should try to avoid doing is constantly changing things for the sake of it. Sure, sometimes the nature of your content might mean that it's only relevant for a short time and so you need to be updating it all the time, and that's fine because that's what your site needs. But if there's no reason to keep changing it other than poor planning or being indecisive, then it's not such a good plan. Better to spend a bit of time working out what you want on there and get it right in one go than to be going back and fiddling around all the time.
Note – I'm not saying you shouldn't edit your pages or correct mistakes! If you see a typo or there are little tweaks you want to make, that's fine. Any time you see something like that, fix it. What I'm talking about is making bigger changes, particularly changing entire pages – doing that is likely to confuse Googlebot about what you've got on your site and where it is, and if it keeps going to pages and finding the content it expects isn't there, it's likely to lose interest very quickly.