Removing files from your HD will not make it faster. It's only bits, not "stuff" that adds weight. It makes no difference if your disk is empty or full, it performs the same.

Defragmenting can help performance a little, but it makes less difference on modern ZBR, LBA drives than it did in the past. I use PageDefrag to defragment the registry and paging files. Windows' defragmenter can't do this.