One thing you will need to understand on a drive with several Partitions: ANY Partition MUST be one contiguous chunk of space on a hard drive unit. So the only way you can extend an existing Partition is if the space RIGHT AFTER it is NOT already allocated to another Partition. In other words, that space you want to add MUST be Unallocated Space.
Usually if you have two or more Partitions on your boot drive, the FIRST one is C:, and the second Partition is placed right after C: so there is no Unallocated Space adjacent to C:. If that is your case you will need to do this in two or three steps. First you'll need to find out how your Partitions are organized so you know which one is right behind C: and needs to be cleared out. Then you will have to make a complete backup of ALL the data on that Partition ("drive"). Maybe you do this to a different disk unit like an external; maybe you simply copy it all to another Partition (drive). Once you have your data safe someplace else, you will need to Delete that Partition so that it becomes Unallocated Space. THEN you can go about expanding the C: Partition into that space.
Now, for simplicity I assumed that the Unallocated Space you could create this way will just match up with the amount of space you want to add to your C: drive. If not, it is more complicated. If it is a little too big, just use it all anyway. The only thing you could do with a leftover block of Unallocated Space in the middle of a HDD unit would be to Create there another Partition to be a small drive. If the Unallocated Space you freed up above is too SMALL, then you will have to repeat the basic process to empty out more.
A major re-sizing of all your Partitions could be done with external backups, deleting all Partitions, creating new ones, and then restoring from the backups. But I doubt you need to do anything so long and complicated.