So you need to update your core or install a blogs version compatible with your core version.
Here you can find the different blog plugin versions: https://github.com/oxwall/blogs/releases
+1 Darryl B
1.- Oxwall 1.8.4 need PHP 5.5, you need to have this php version or php 5.6 before make the update. And make sure that your new php version meets the requirements. You can see the PHP requirements on the right place of this page http://www.oxwall.org/hosting
If your website is already running on php 5.5 or 5.6, then you don't need to change the version.
2.- Sometimes the default PHP configurations are not enough, you need to increase your PHP limits (memory limit and time limit) before run an core update to make sure it completes properly.
3.- Make sure all your plugins works on the latest version, if you go to the store and read the 3rd party plugin's topics (paid plugins and free), in some of them you can see people complaining about compatibility issues with the latest version, look for your installed plugins and if they say that it is not working on the latest version and it is not fixed yet, then maybe it is true. So be careful on that. If you need plugins that are not working on the latest oxwall version, you better not make the update, because that plugins will be unusable and you will have to uninstall them.