I get an ERROR message to the effect of the file is being used s/where else....like WHAZZUP ?

I can re-name some files, but some I cannot. I know I should re-name them at the point of d/loding, but s-times forget...then when I want to ORGANIZE my files with the same Bold & hyphens, etc... some files, it won't let me do it..

So, again, Q: how do I make the file NOT in USE s-where else in my computer? Thx!