Topic was moved from Installation Troubleshooter and Server setup.

Marcus, it would be better not to wait for long time to update your software. In your case before you attempt to update, make sure that you:
- Make back up of your website;
- Run the platform update first, till updating all available plugins;
- Run theme update also only after the platform update.

Also you can use this steps to perform the update in right order:

1. deactivate all third-party plugins.
2. turn on 'Maintenance mode" in Admin Panel >Pages&Menus > Maintenance Page
3. enable DEBUG mode ( set to "true" in ow_includes/config.php)
4. perform platform update.
5. update all native Oxwall plugins. Don't check your site until you update all of them
6. update your theme.
7. enable DEV mod in ow_includes/config.php
8. Turn "Maintenance Mode" off.
9. refresh any site page and disable DEV MODE: define('OW_DEV_MODE', false);

Thanks teresa so much love your replies!

Also after all this steps done, enable all the third party plugins one by one. After each plugin enabled/updated - check site. Better to carry out this process in dev mode. If some of the plugins crash Your site - disable it back and proceed with next one up to the end. After that disable dev mode and contact plugin developers to fix broken plugins.
BEFORE UPDATE: copy all the modified file in plugins and core file or make notes what changes You made with them, as all the plugin and system files will be overwritten after update. Example: StartPage Pro has hand made themes. After update all of them will be refreshed. Also if You change css file for mobile version it will be refreshed - save it before update.

Thanks buddy! Will this update affect somehow my custom theme not the ones that come with the script?

Also Is there a way to find out what extra CSS will be added to global.css file?

Custom themes are not changed during script update. But they can be changed during update by theme developer notification. If this theme based on some third party developer or by You  - no problem. But if it's a modified standard theme - make backup and then replace after update. In any way I try to make backup before each update of script or themes.

Quote from Marcus
Also Is there a way to find out what extra CSS will be added to global.css file?

Use some good code editor. First You need to download css from Your server. Then download fresh installation archive and extract same file. Then compare this two files using code editor like geany of other.

You are awesome thanks so much! How can I bring my custom theme up to date since it's no longer supported?

It's the most interesting and difficult question. You should find some info about all the changes in files, which have been done since Your last working version. The other way is just take new base theme (latest version) and modify it by replacing some part of code from Your theme. Actually You have to build Your theme again. The third way is to launch Your old theme on test website and fix all the problems one-by-one. No more ideas... For this question You should contact oxwall devs.

Thanks so much buddy!

My theme only contains 2 HTML files and CSS so I just need to check those files against 1.8 default version right?

I can see two ways:
1. Check if Your theme working without changes (if not - compare and try to fix)
2. Build it again

Yevhen, thank you for your assistance.
Marcus, if  you have further question concerning the theme compatibility after platform update,  it would be better to create separate topic.