Renaming  files one by one may take longer time to complete. The trick here shows you how to rename multiple files simultaneously in Windows.
Why not apply this trick for use? To rename multiple files at the same time, hold the CTRL key on your keyboard and select any of the files you wish to rename.

After that, right click on any one of the selected files and select Rename.
Now, type a name for the file. Alternatively, you can use the F2 key to rename your selected file.

Once the procedure of renaming is completed, the names of the selected files will also transform to the name identical as the name you typed just now, except that numbers will be appended to the end of name sequentially.

For example, these are the files I wish to rename to "colorful".

The files are selected, right click on one of the file to rename.

The rest of the files will also be renamed and appended with numbers respectively in series.