Hello, this is Emily.
First of all, if this is a chromebook, it is not Windows you would be having on that device, because chromebook runs on their own operating system from Google.
If this is a Windows operating system, then what you have is not a chromebook but probably just a regular laptop.
Regardless, 30GB is not a lot for either operating system, and it is not something you can do from the operating side. You need to upgrade the hardware, particularly the drive (whether it is harddrive or SSD). Contact the computer's manufacturer support. They can help you identify if the device can support an upgrade of drive and what type of drive you need.