The real issue is the HDD over time gets fragmented. Getting a defragmentation app to undo the fragmentation or backup the drive fully and reformat it will also work.
Replacing your HDD with SSD is also a good direction or what I would do is add the SSD! [guide|6634] That way I can make the SSD be the boot drive with my apps and leave my stuff on the HDD. That way you don’t need as large a drive! A 250 GB would be more than enough for most people!