Download GParted. Burn a disc from the ISO.
Shrink the third partition to accommodate for the amount of space you want to expand the first two partitions. Move the third partition (to the right, or rather to the other side of the now unpartitoned space, since you will need to expand the second partition into this unused space). Resize the second partition into part of this unused space. Move the second partition to the right to leave the remaining unused space available for the first partition to be expanded into. Resize the first partition.
The reason for this is because the partitions start and end in specific places on the disk and all data within a partition is contiguous (kept together). Although you have free space, you cannot use it to expand your C: partition because the free space you have is not immediately after your C: partition on the disk.
You should have no issues doing all of this before you have to apply any of the steps.