Hello and thank you for downloading!
I'll take you through how to use the mod without any issues.

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1. Open the downloaded folder and extract.
2. Open the folder and find the style you want (for example 'Joja')
3. Find the content folder.
3. Open the content folder and then find the sub-folder of the type of feature you want to retexture (for example 'Buildings')
4. It should then come up with a load of .xnb files.
5. Copy the .xnb file you want or if you want all of them just copy them all.
6. Then open your Stardew Valley file which if you're using Steam can be found through the 'properties' section when inspecting the game.
7. When you're in your Stardew Valley file, find the Content folder and open it.
8. You should see a bunch of folders but make sure to look for the open that you copied the .xnb files (in this case 'Buildings')
9. Open that folder and you should see a load of .xnb files like the first one.
10. Replace the .xnb file or files of your choosing by pasting or dragging them into that files and make sure to replace them.
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If you followed that correctly then you should have no issues and will see the changes in game next time you load up.
Once again thank you for downloading and if you have any suggestions or issues feel free to contact me on Nexus - EclipseShad