how do i unpair my remote?

For the Siri Remote: There is no unpair procedure. Any old Siri Remote will be unpaired automatically when a different Siri Remote is being paired with the box – as one Siri Remote can be paired at any given time.

If this is not about the Siri Remote, then please elaborate.

I'm able to change spectrum tv channels with an up & down button on it that I can't do with an apple remote or am I missing something?

You are correct. Spectrum developed their own remote with additional buttons for their special functions in their own app.

I believe it pairs just like the official Siri Remote (Menu + Volume Up), and will then replace what was paired before. Pairing the Spectrum Remote with Apple TV and troubleshooting - Spectrum Support