Another option besides CCleaner to clean Windows files, is Wise Disk Cleaner (freeware).
Over time, junk files, temporary files, all kinds of system files and other items you do not need at all accumulate on your Windows Computer. Those useless files take up valuable hard disk space and slow down your computer. Wise Disk Cleaner can delete these unnecessary files on your hard disk to free up disk space and make your computer run faster. It also provides many custom options to allow advanced users to clean up more files they don’t need. Equipped with advanced algorithms, Wise Disk Cleaner can scan and remove them within seconds, making it one of the most efficient disk cleaners out there.
I use AVG Tuneup to clean my drive. Such programs need to be used with care, and one I used in the past caused problems by being too zealous. That said, it identifies what is unwanted on my computer and asks me if I want to delete it.
AFAIK, you should not fill a disk to beyond 80% capacity, as it gets much more fragmented after that point. (Not an issue with SSDs.) What to get rid of? Look for unwanted backups, check your programs to see if you really need them all. If you have data on the same drive, see what can be deleted, and move some or all of the rest to another drive. Check first if the relevant program has a hard-coded path to the data.
But if your drive is that full, I think you have to look at getting a bigger one to replace it. The same applies if you do not have room on other drives, especially if they are partitions on one disk. You can of course juggle partitions if you have one very large drive and allocated too little to C.
Windows 8 came out 8 years ago, so they weren’t adding new features to Windows 7 after Windows 8 came out–only bug fixes.
OP: there are a lot of options; perhaps you should tell us more about your situation. Last year I purchased a somewhat similar laptop, Dell Latitude E6430 manufactured in 2012-13 with 128 GB hard drive and Windows 7 and I replaced the hard drive with a 256 GB SSD hard drive and upgraded to Windows 10. There are Youtube videos on how to do the hardware replacement. But doing the software installation with all the programs I use was very slow. [I copied all the data onto an external portable drive.]
Years ago, my dad had a similar situation on a computer that should not have had that much on the hard drive. He had been burning a lot of photos to disk and it turns out his computer was also storing multiple copies of each high resolution picture to his hard drive.