Upgrade WordPress 2.8.6 to Word[ress 3.5.1

Can I just pull the trigger?

Not with risking damaging your database no. That’s far to large an upgrade to be carried out in a single step. As you have such an old version of WordPress, you will need to carry out a series of smaller manual upgrades. See Upgrading_WordPress_Extended for the full details.

Glad I could help. Good luck with the upgrades. 🙂