The category "Other" in my Storage takes 4GB out of 6GB on my Internal Storage, any way to clean it?

I have HTC One S. When I open my Storage , it says : 4.10GB/6.07GB ; Apps: 220MB ; Other : 3.88GB ; Available: 1.97GB . That's after I restarted my phone on Backup & Reset. I did it several times , and it doesn't change. I'm clueless. I don't have any ideas on what could take that space , nor how do I clean it (properly ofc.). I was looking on the internet for a whole week, and still have found nothing useful. I have tried Clean Master. It doesn't make any difference in the "Other" category. Still the same. It is a old phone , my dad was using it for 1/1.5 years , but I don't think it has any influence on the current memory , after resetting the phone. Only the "Apps" is clickable in Storage. In other words - I cant click on "Other" to see what's inside. I tried an app called "Disk Usage" , and it says: 1)When I click on app storage : Applications : 220MiB ; Data : 2236MiB ; Free space : 2016MiB . Now , 2)When I click on Storage card: Storage card: 10171MiB ; System data... Android... (and many more little stuff) ; Free space 10164MiB... I'm not worried about my phone storage - on storage card. I'm worried about my internal storage , which is, I'm pretty sure , showed on app storage. The big thing : FREAKING 2236MiB FOR DATA? It has to be Data that's messing me up. Data is lost when resetting the phone with erasing al the data , right? I did it several times , but still , the category "Other" still doesn't change at all. From this , kind of a bigger talk... well to read it is big, right? Never mind... Again , from this bigger talk , I actually only want to know the answers for two questions : What is on "Other"? and , How do I clean "Other" Thank you for responding in advance. https://onedrive.live.com/redir?resid=ABE64B8B54D4B3FA!3407&authkey=!AEzUeDYmxJnRCo8&ithint=folder%2c (here are the pictures)