Hard drive upgrade to SSD?

You might want to look at cleaning your current HD of unused items which are taking up space. Once you have cleaned house think about defragmenting your HD as the fragmentation is a major cause of slowness. Of course make sure you have backed up your HD and run Disk Utility to make sure the drive is healthy.

I would do this first before thinking about upgrading the storage with either a new HD or SSD.

While SSD's have speed & durability they do have a failing that of space. A HD on the other hand is able to store much more data than a SSD can today, but they are sensitive to being banged and can be slow when they are not maintained.

Conceder the Pro's & Con's of any storage solution beforehand.