The partition C is of 176 GB, or the whole hard disk? If you have a recovery partition, then some space might be used up for that.
You should take proper backup of your system before proceeding with softwares like Partition Manager. Things can go wrong, and it is advised to have a working image of your hard disk, and/or also a backup... so that you are able to restore your laptop as it was.
To find out where the space of your hard disk is being used up, I would suggest using softwares like
WinDirStat, or
TreeSize. These softwares will help you see the disk usage in various files, and folders in a graphic way. This makes it quite easy for you to figure out, where the space is being used up. You can then take appropriate measures.
Do you have any other partition besides the C drive?