First of all you've got to be sure your SD card contains the matching db file inside the SD\Garmin\SQL folder, otherwise the GPS won't show the Trails menu option. If you can search for named trails in Basecamp you should also have the option in your 450.
Now it's important to have the latest firmware offcourse and set Activity to Hiking or Mountainbiking.
Since I don't have an Oregon 450 by hand I am not shure if the Trails option is inside your Main menu or elsewhere.
On My Oregon 600 it's here: Where To? > Trails.
On my 62s it's behind the FIND button: Find > Trails

Now that you probably have it working it's very well possible that the Trails menu tells you there are no named trails because your position is too far away from the actual trails. This is the case if you are searching for trails in another country, I can't search Alpine trails in the Netherlands for instance. After setting the cursor in the right area the Trails menu will show some trails. I think there is some kind of distance filter because I never get all trails at once.