Get the song file in a digital audio editor or DAW
Check whether you have a true instrumental or only a vocal mix
Use an official instrumental, karaoke, or acapella if available
If you have stems, mute or remove the vocal track
If you only have the full mix, try vocal isolation tools
Apply center-channel vocal reduction if the vocal is centered
Use phase cancellation methods with an instrumental or acapella version
Clean up leftover vocal artifacts with EQ, noise reduction, and editing
Rebalance the mix after removing vocals
Export the result as an audio file
Test the instrumental on headphones and speakers
Save a backup of the original song file