I can see some images added to the content of the slider in the grid gallery:
how can I remove them?
These images are most likely displayed because you have added a WordPress gallery in the content of the portfolio item – when you add images, they should be added as attachments to the portfolio item, but you shouldn’t click on the “Add gallery” button below the uploaded images set. So, if you have added a gallery in the content of the item, it should look like this:
and if you have this gallery into the content of the item, you just have to delete it and these images won’t be displayed anymore.
If, however, this is not your case and you don’t have a gallery inserted in the content of the item, you can also try to temporarily disable all the plugins installed, as this may be also caused by one of them.