Unfortunately that's the entire size that you have,128GB or 256GB (minus whatever windows and your programs are taking up).
We have recently had an evolution from mechanical hard drives (similar to a spinning DVD encased in a steel case) which had huge amounts of storage as much as 2 Terabytes (TB) of data in a laptop. We have now evolved to a "better" hard drive system which is "solid state" no moving parts like a really high performance internal USB key/flash drive.
HOWEVER the new solid state drives (SSD) are smaller, 128GB (or an eighth of a terabyte) for SSD as a starting point vs. 1 terabyte on average for a mechanical drive. 10x as fast and 1/10 the size, it's purely a cost issue, the cost of a 1 terabyte SSD is $1000 (at the time of writing) just for the disk alone vs $85 (at the time of writing) for what you normally get in a standard computer.
This is a new struggle that we haven't had for years and years there are a few options as to what can be done, firstly make sure you don't have any videos or other huge files on there don't need DVD movie backups etc need to go elsewhere.
Second, for data that you won't be using all the time you can archive it on Microsoft OneDrive you will have probably 15GB - 50 GB of free OneDrive storage with your Microsoft account which is highly integrated into windows 8.1. Just make sure it's not all set to automatically synchronize "offline" back down to your laptop again otherwise you won't save anything. Here are some resources to get started on this:
(Just from a random Google search)
Lastly, the bulky data, huge video files, DVD backups and the like you can leave on an external hard drive (pocket sized drives to up 2 terabytes) or USB keys up to 256GB (or a quarter of a terabyte) for those occasions when you need it. It's a little unwieldy having to plug something in but with USB 3.0 the speed is around the same as with the data directly on your computer (depending on the quality of the external storage).
Just remember that a single USB drive with data on isn't a backup, a backup is a second copy of the same data see here for my rant on this.
Hope that helps, if none of these solutions are workable, there is one last option which is removing the small SSD in your new laptop and replacing it with a larger one.