Please find out steps below:

- You need back up your site (database+code), if back up make error you can use back up file.

- Copy your custom code which you change in your code.

- Download new version theme, uninstall old theme and install new theme.

- Deacitve and remove plugins which request to install in your site (this is our plugins, not plugins which you install after).

- click Begin installing plugins: prntscrand install plugins again (this is new version which we changed code and you need update them).

- Paste your custom code in new theme.

- Check your site again to sure it works.