If you can open the zip file, open the file texmod.txt . It will contain the adress of the images so there you can delete the ones you don't want (if you only delete the .dds images you will get an error when loading the mod).
If you want to replace the existing ones, replace the .dds file you want with yours.
If you want to add a new one, you have to find the adress of the image. To do that, go to your Hearthstone collection and find the card you want to change the art (go into craft mode if you don't have it). Now go on umod and set a key for the Back, Save and Next button.
Here i use the arrows. Now check the Save single texture button, set a path directory to save the image and click on upload (at the bottom of umod).
Once it's done you should have the number of textures on the top-left of your hearthstone screen.
You now have to use left and right until the image you're looking for become colored. Once you found it, press the save key and look in your directory the name of the file wich contains the adress of the image.
Exemple with Living roots
You get the file
The adress for the art of living root is 0X539E25AD (always start with 0 and an x)
Now you can add the adress to texmod.txt similarly to the others with your own .dds file.
If you wonder how to save images in a .dds format, google is your friend i guess.
If you want to replace the existing ones, replace the .dds file you want with yours.
If you want to add a new one, you have to find the adress of the image. To do that, go to your Hearthstone collection and find the card you want to change the art (go into craft mode if you don't have it). Now go on umod and set a key for the Back, Save and Next button.
Here i use the arrows. Now check the Save single texture button, set a path directory to save the image and click on upload (at the bottom of umod).
Once it's done you should have the number of textures on the top-left of your hearthstone screen.
You now have to use left and right until the image you're looking for become colored. Once you found it, press the save key and look in your directory the name of the file wich contains the adress of the image.
Exemple with Living roots
You get the file
The adress for the art of living root is 0X539E25AD (always start with 0 and an x)
Now you can add the adress to texmod.txt similarly to the others with your own .dds file.
If you wonder how to save images in a .dds format, google is your friend i guess.