Processors and RAM are fixed entities in a PC, but right from day one data is incessantly eating away at your storage space. And it's not just your data (which you can manage) but endless gigabytes of temp files and cached junk.
On a desktop system with multiple gigabytes of storage you might not notice this, but on a notebook that still has a drive measured in megabytes each byte is precious. However, no matter how carefully you manage the space, one day whatever storage space you started with won't be enough.
This is the day you start thinking about upgrading the drive in your notebook.
I wish I could give you advice on carrying out the actual upgrade on your system, but I can't because every system if different. Sometimes it's dead easy, you need special tools, sometimes there are tiny (but expensive) parts waiting for the chance to be broken, and sometimes you have no choice but to dismantle the machine down to its constituent atoms.
My best advice here is that you do your own research. Check out the splendid repair guides over at iFixit, or scope out YouTube to see what others have done. There's a lot of information out there. And remember, if you do decide to carry out the upgrade yourself, take care, because if you break something, you own both parts!
As to what hard drives you can use as a replacement, well that I can help with. There are some splendid drives out there you can use.
Before you buy a drive you need to know what thickness your system takes. Notebooks take 2.5-inch form-factor drives, but the thickness can vary. As a rule most older notebooks took a 9.5mm drive, with 7mm drive fitting most newer notebooks, while ultrabooks need a super-thin 5mm drives.
Some of the best replacement drives out there are the Seagate SSHD hybrid drives that combine a standard hard drive (HDD) with a solid-state drive (SSD). This way you get the best of both worlds - the capacity offered by an HDD and the speed of an SSD. They come in a range of thicknesses, with the 9.5mm offering 1TB of storage, while the 7mm and 5mm options come with 500GB of storage.
Prices start at around $65 got 500GB.
If you're after something with a little more oomph then I suggest taking a look at the WD Black². The WD Black² is the world's first 2.5-inch dual drive storage solution, offering the HDD and SSD storage as separate drives. The drive is aimed not just at gamers but at media professionals who work with video of RAW photo files.
The WD Black² comes with 120GB of flash storage and a 1TB hard drive and will set you back $130.