Would you like to see instructions on how to make topless and bottomless variations from dressed and nude originals?
Install gimp
https://www.gimp.org/
then open it.
Click on File -> Open As Layers and select the images you have.
Go to Windows -> Layers and make sure the image with the naked girl is below the other image.
Duplicate the dressed image twice and rename the layers "top", "bottom", "dressed", "naked".
Right-click on all the layer names and click on add alpha channel.
Open a Toolbox and select the Free Select tool.
Click on the layer called top, and click on the eyes of the other layers until only the layers naked and top are visible.
Make sure the layer "top" is selected, and select around the top, leaving some space.
Then ctrl-i to invert the selection, and delete to remove it.
Do the same procedure on the bottom layer, selecting the bottom.
Example from Dakun Art
Finally, select the layers you need (naked and top or bottom) and click on File -> Export to save it.