There’s not really a “bump feature” like something you can just click. For normal non-wiki topics, bumping happens naturally when someone replies, and there’s Configuring auto-bumping for topics on a per-category basis.
A way to do it manually is by changing the timestamp as described here – although re-dating topics could cause confusion.
(You may also notice the Reset Bump Date option on the topic wrench menu. This basically un-bumps a topic if you don’t want a reply to move it up on the topic list.)