How to Install Scripts to Aseprite v1.2.10
In Aseprite, click File -> Scripts -> Open Scripts Folder. A folder should pop up and that's where you're going to be dragging the lua files into. After you add the files, make sure to restart Aseprite so Aseprite shows it in the Scripts menu.
How to Install Scripts to Aseprite v1.2.9
The section below will teach you how to install scripts to Aseprite v1.2.9! However, you can't use .lua files with Aseprite v1.2.9.
Locating the Aseprite Folder
First, we need to open the folder where Aseprite is installed. To do this, go the the edit menu located at top of the Aseprite program. Then click on Preferences that should be at the bottom of the menu.
A preference window should pop up and you need to go to Extensions located at the left side of the window. You should now see a list of palettes. Click of any one of them and click the Open Folder button.
A new window should pop up but we need to go up a few folder to get to the appropriate location. Go back a folder until you get to "data" folder.
Modifying the gui.xml file
Now we need to modify the gui.xml file so it shows the scripts in Aseprite. You will need to get a text editor that's better than Notepad. Notepad++, Atom, sublime, or whatever you're comfortable with. MAKE SURE TO MAKE A BACKUP OF THE FILE then open it in a text editor. Search for the word "Scripts" and you should see something like "<!--menu text="Scripts">". We're going to remove !-- and --. It should look like this at the end.
Now we want to add some items to it so we can run custom scripts on Aseprite. This is an example for Pixel Stats.
Save the file and go back to the data folder.
Adding Script Files to Aseprite
Back into the data folder. Find a folder named "scripts". You just need to put the script in that folder and you're done!
Now close Aseprite and re-launch the program. You should now be able to see a new option in the Edit menu.
I'm still having issues...
If you're still having issues, take the backup of gui.xml and restore it. You can contact me in the Aseprite Discord if you have any questions.