Hi, unless you know what you are doing it is not a good idea to remove anything from the windows folder, certainly you should not delete the installer folder (hidden by default) you can move data to any of your internal or external drives (be careful as external drives can be assigned a different drive letter (it is possible to prevent this, however I am certain you don't know how) it is better to do this internally.
Your installer folder is so large because you have moved program files to another drive, this is a job for expert users only and I do not recommend it. it isn't needed, you have plenty of space on your other drives use it. You can save space on c: drive by moving pictures, videos, music data etc etc.
I think you would be better off if you backed up your data and did a fresh clean install of windows ten. Keep OS files on the c: drive (this includes program files) just move data to the external, or internal extra drives.
You do not (and you should not) use third party tools for this, they are not needed (post #4).
Go to search and type:- command prompt, right click on the returned command prompt and select "run as administrator" an elevated cmd prompt will open, run the following cmd, it opens the advanced disk clean util, check the boxes you want to remove data from (each box has a following description) all boxes can be safely checked, although some you may not want to clean (don't check the box next to an ESD drive).
%SystemRoot%\System32\Cmd.exe /c Cleanmgr /sageset:65535 & Cleanmgr /sagerun:65535
Press enter, select your options and allow to run, be patient and let it run, it can take some time and appear to hang, it will complete, this will remove a lot of unneeded files.