ffmpeg – Increasing Volume of Specific Audio Track?

I’m a complete newbie when it comes to ffmpeg (I found out what it was 2 days ago).

I ripped a show from from a Blu-ray disk; The episodes were dual audio and had subtitles encoded in them. When I try to increase the volume of a specific audio track, the subtitles and remaining audio tracks get deleted!

How do I up the volume of one audio track without touching the other tracks as well as keep the subtitles?

Also, since there’s a few episodes, is it possible to do batch conversions?

Hope to hear from you soon!