Always at some point you need to make a massive renaming of many files, either to assign them a name for the first time or to apply small modifications, instead of doing it manually (tedious and boring work where they exist) you can use a practical tool like Bulk File Renamer 1.0 which will automate the entire process.
Allows you to automatically add a numerical sequence to the files (both as prefix and by suffix), rename from uppercase to lowercase, etc. It comes equipped with a preview that allows you to see the results before applying them and thus be sure if these are the changes you want to make.
You can free download Bulk File Renamer 32, 64 bit and safe install the latest trial or new full version for Windows 10 from the official site.