How do I center a new track?

Meaning…

I have 1 song. I cut 30 sec. out of the middle and want to replace it with the 30 sec track.

The audacity screen is open.

Top track is the new imported audio (30sec.)
Bottom track is the track in which I want to insert it.

So, How do I move the track from the left side of the track bar to the center OR how do I insert it into the silenced section of the bottom track?

The instructions vary depending on which version of Audacity you are using and which operating system.
Example of an Audacity version: “Audacity 1.3.13 (Unicode)”
You can find the version number by looking in the Help menu > About Audacity.
Example of an operating system: “Windows Vista Home Basic 64-bit”