Is there any data on the drive that needs to be backed up? Do that first. If you're dual-booting, I'd back up Windows files, too. Partition editing can be incredibly destructive if something goes wrong or you make a mistake.
And then, what OS will you be using to delete the partition(s)?
In Windows, you'll want to use "
Disk Management".
To delete the partitions from Linux, you'll need to boot off a Live CD or Live USB drive, since you can't delete a partition in use. And when you boot off a partition, it's most definitely in use. Then, from the Live CD/USB, start gparted (main menu > system > admin > partition editor). Right-click on the partition you want to delete and delete it.
If you're dual-booting with Windows, you'll probably want to grow the Windows partition to fill the newly freed space. gparted can do that, too. Just right-click on the Windows partition and choose resize/move after deleting the Linux partition.