Shopify theme updates have always been a real trouble for the store owners. We have prepared a video tutorial for you on how to upgrade Shopify theme in a most convenient and stress-free way.
Of course, never publish and THEN update theme, but take unpublished theme and use preview mode to check if the new theme looks exactly how you want before publishing.
Fastest way tutorial
Official Shopify tutorial
Here is an official tutorial so you can understand more clearly.
(without copying code in settings_data.json file)
- Copy all your images from assets folder of the current theme you have, to our new theme, before uploading (Shopify just override default theme images with the image you upload so they have a same name). Otherwise you would need to upload home, slider, banner and parallax images again.
- Open theme customize of your current version in one browser tab, and then open the theme customize of the new unpublished theme (the new one with updates that you just uploaded) in the second tab and then check the settings and copy paste text etc. Once done you can preview new theme (small eye icon next to unpublished theme) and see how it looks before going live with it. It should take no more than half an hour of your time, depending on which theme settings you are using.