Windows 8.1 How do I repartition my 80 GB Laptop HDD?

Just a general thought on partitioning--there are certain arguments for putting the OS and software in a partition separate from your user files. However, every time you partition a space, you introduce constraints and inefficiencies for using the space. Long before you fill the partition, you will run into situations where the free space remaining constrains doing something (many processes require much larger temporary space). The partition has no flexibility to deal with needs as they arise.

Also, whatever allocation you pick between the partitions will never make the best use of the total capacity, especially if you arbitrarily split the space in half. If you start with a humungous drive that you will never come close to filling, this isn't an issue. But if you start with a small drive, partitioning will make the capacity constraints worse.

It doesn't sound like you plan to do the kinds of things for which partitioning is important (like a dual boot). Within the capacities of laptop drives and for the type of use it sounds like you are planning, you might be better off not partitioning (with the exception of something like a protected recovery partition).