Hi @Claus_LUO !
I hope you and your family are doing well during this Covid-19 pandemic!
If you want to update your theme but have edited the code or installed an app that has changed the code, then you need to manually add an updated version of the theme to your online store.
In order to achieve this, the first thing you need to do is to create a backup of your old theme so that you can discard your changes and start again if you need to. Then, login to your account on Shopify Theme store and search for your theme. Click Add latest theme version or Add theme.
After that, you can customize your theme by using the Theme editor and publish it.
Note: You might have to uninstall any third-party apps that add codes to your theme then reinstall them. Go back to your original copy of the old theme and copy any additional codes and add theme in the corresponding position on the new theme. If you are not sure whether you have to uninstall these apps or where to paste the codes, you can contact the app developer to get support by clicking Get support from the Apps page on your Shopify admin panel.
You can find a more detail instructions from Shopify help center.
I hope you will be able to pull it off! Good luck!
Hi there @Claus_LUO!
Don here from Shopify.
The first thing we woudl advise from here would be to duplicate your current theme as it is so you have a copy to work from when you upgrade your theme.
Then, when the new theme has been downloaded you can refer back to the original copy which will still have the third-party code present.
You would need to copy any additional code out from the old copy of the theme and add it to where it needs to go in the newer theme.
If this code was added for an app or by a theme developer, you can reach out to them for any support you need with ensuring it is placed correctly in your new theme.
There's more info on updating themes here on our help site that you can check out.
All the best!