The best way to make changes to the WP-Drudge theme without breaking the ability to upgrade is to create a child theme. This lets you override one or more theme files while keeping the rest intact. When you upgrade, the parent theme is modified and your changes stay in place. Otherwise, you’ll either have to stick with your older, modified theme (might be problematic if we release security fixes) or keep track of what was modified for each upgrade (hard to do and prone to mistakes).
How? Your child theme will hold files that take precedence over the parent theme. The WordPress Codex and the Theme Developer’s Guide are great resources for learning about how this works in-depth. You can also use our child theme sample below to get started.