How can I change the ALT and names of the images that are not of products : images of the homepage, of the blog, etc... They are all in Settings / Files.
For the images that you upload to Theme / Customize:
For the Blog use the following steps:
Change the ALT tags of other images in the same way.
In regards with the Title of the images, check if the image name is correct before uploading it to your store.
Hope it helps,