You can't change the block size; it's whatever the drive presents (512 bytes unless it's a 4K native drive, in which case it's 4096 bytes).
Sectors are the same thing as blocks, just a different name.
Clusters are the file allocation granularity. The default for NTFS is 4096 bytes. Tiny files will disappear into the NTFS file record (always 1024 bytes) so for them, it doesn't matter what the cluster size is.
Large files do not necessarily consume many extents (not if they're contiguous), nor does the cluster size much affect this.
You cannot change the cluster size on an already-formatted volume. You'll need to create a new volume with the parameters you want and copy the data to that volume.
Let's say you have 3 million files and due to the default cluster size each wastes an average of 2048 bytes. Then your total wasted space is 6 GB. This is 0.6 percent of a 1 TB disk, a smaller percentage of a larger disk. Suppose it's a 2 TB disk that cost you $100; the total cost of the wasted space in the last allocation clusters of all of the files is then 30 cents. Less if a lot of them are stored completely in the file records.
Most of us stopped worrying about it long ago and just let NTFS use its default. Besides, having the cluster size match the processor's page size is convenient for Windows' Memory Management code.