De-partioning Harddrives

Dell OptiPlex 5040 i7-6700 CPU, Windows 10 64-bit. I was trying to get some use out of several SATA hard drives pulled from older PCs. The hard drive is a Seagate Baracuda listed at 250 GB. When I access it with a docking station, the computer only sees 180 GB. Can I de-partion this hard drive to use the entire 250GB?

 

Try Minitool Partition Wizard: http://www.majorgeeks.com/files/details/minitool_partition_wizard_home_edition.html
I've used it to format discs with Linux and Mac OS partitions, which Windows doesn't support.

 

I've had great luck with EASEUS Partition Master Home Edition. Note it is free for home, non-commerical use.

Although I have never lost any data using this tool to shuffle partitions around, any time you mess with a disk's partition tables, the risk of data loss is great. A sudden power interruption is all it takes. So make sure you back up any data you don't want to lose first.

 

If you do not have anything you wish to save on it, as Digerati reminded you, then Windows disk management will allow you to clean the disk.
It may well be that the second partition is hidden-Patition Wizard (as JustPlayin says) will give you an option to unhide it- it could also be a recovery partition. e first
Either way, if you just want a clean formatted disc, then delete the second partition first,and then extend the C:drive to cover the whole 250gb.
If you are not using this hard drive in its original pc/laptop, then you can fit it into another pc, use a windows disc and simply use the setup disc to delete all partitions, then create a single partition, and install a fresh system on the pc.
If you wish to use it for data storage, then simply format it.