First of all: There are two partitions, not one.
And yes, you can change the partitions. Boot a live system (so the hard drive isn't accessed) and open GParted. Resize the big partition from the right and you have space for more partitions. Resizing it from the left to the right is also possible, however, this will take a lot longer since all data has to be copied.
It is also important to mention that changing something on your partitions always comes with a risk, especially if there is a power failure and you're not working on a laptop with a battery or behind an uninterruptible power supply.