To change the number of Post Revisions stored by WordPress…
As with most things WordPress, the easiest way to limit the number of post revisions is to use a plugin. Simply follow the steps below if you would prefer going that route:
1 – Log in to your WordPress Dashboard.
2 – Click Plugins>Add New.
3 – Type limit post revisions into the search box. You should now see a bunch of plugins to choose from.
4 – Select the plugin you wish to use and click the Install Now button.
Note: Most “limit post revisions” plugins allow you to set the maximum number of post revisions that WordPress will be allowed to create for a given post or page by changing a setting on the plugin’s “Settings” page.
That’s all there is to using a plugin to limit the number of post revisions WordPress will create on your blog.
All of the above being said, avoid using a plugin when there are other ways to achieve the same result, for two reasons:
1 – Every plugin that’s active on a blog slows the blog down by a bit.
2 – Every plugin that’s active on a blog is another potential entry point for a hacker to take control of your blog.