If you want to delete datasets from the system, you have two options.
Note: If you are not sure whether you want to permanently delete the dataset, you may also make the dataset private on the system. Please keep in mind that by making it private, any chart that used that dataset will become blank. You as an admin will still see the dataset in the data catalog, but non-admin users will not.
Option 1 – From the dataset - if your dataset was uploaded directly to the portal (local)
The first option starts with checking whether there are any system dashboard reports built using the dataset you plan to delete. If so, you will either need to replace the affected dashboard(s) and/or chart(s), remove them, or set them to ‘private’ temporarily until you decide a permanent course of action.
Once you have verified no dashboards use the dataset or you have revised affected dashboards, open the dataset, select More Actions > click Delete button at the bottom of the page.
Option 2 – From Admin panel > Datasets - if your dataset was added from Knoema
Note: there are two ways to understand that one or another dataset was added from Knoema:
1 - In Admin panel > Dataset you'll see Category - Knoema - Automatic / Knoema - On-Demand / Knoema - Manual 
2 - Open dataset in Dataset Viewer > click more actions. And you'll see only one or two options instead of Upload dataset/History/Add segment ect. And of you click on Edit details, you'll a link to Knoema dataset.
The second option for deleting a dataset is accessing Admin > Datasets, selecting the dataset, and clicking Remove dataset.