Download a MIDI sequencing program if you do not already have one. You can use most major digital recording program like Cubase, Logic and Pro Tools, or you can use a MIDI-specific program like Midisoft Studio, MidiSwing or VMPK.
Open your sequencing software and select your MIDI file. Depending on the program, you may need to click (File > Open) on your menu bar and select the file, or click a button on your screen that reads "Open" or "Open File." If using a multi-track recording program, you may need to create a new project and drag your MIDI file onto the project window. The individual MIDI tracks will automatically appear as horizontal bars along your screen, each track indicating a different instrument or layer.
Locate your piano track(s). Each track should contain a "Mute" button and a "Solo" button, sometimes indicated by the letters "M" and "S," and sometimes indicated by different colors. Click the "Solo" button on any track to isolate it from the rest of the recording then press "Play" to hear what the track sounds like. Listen to each track until you find your pianos. In some cases, the word "Piano" may already appear in the left column of each piano track.
Remove the pianos. To remove an entire piano track, click the track title in the left column to highlight it, then locate the "Remove Track" or "Delete Track" option, sometimes appearing with your menu bar options, and sometimes appearing as an option directly on your software window. To remove the piano data without deleting the track, drag your mouse over the MIDI notes appearing on the track (they will look like dots or or squares on a horizontal grid) and click "Delete" on your keyboard.
Save your file. In some programs, you will need to export your project to create a self-contained music file. Locate the "Export" or "Bounce" option on your menu bar, select it with your mouse, choose a title and a format, and click "Save" or "Export."