How to rename files by batch?

I use OI file manager, but I would like to know if there is a way to remove spaces from file names and replace them with underscores, preferably in batch mode? I would even be willing to perform this operation on my windows laptop, so this isn't specifically an Android question, though I'd prefer to do this on my phone. I'm a graphic artist and I have thousands of inconsistently named images in various places, and I'd really like to avoid doing this manually, one by one, as it would take months!