1. Cant upload the theme for installation
If you keep getting error when uploading the theme, its most likely due to small maximum upload size set on your server, this is how you can get around it:
These settings will let increase the maximum upload size along with other settings you may need in the future.
If the maximum upload size is not the case, then you must have download the complete theme package and not extracted it first. Themeforest let you download the wordpress theme or the whole package which includes the theme zip, screenshots, documentations and other files, if this is the package you downloaded you need to first extract it and then find the theme zip you can upload for installation. If you downloaded just the theme then you are ok.
2. Theme settings changed after the theme update
If you updated the theme and the theme styles changed back to the original settings you can just go to the theme options page and hit Save Changes. This will bring back all your theme settings:
3. Error shows up when saving the theme settings
This error probably shows up if you did not properly fill in a field, you should see a notification on the tab or a field where the problem occurred. It should look something like this:
If you click on the tab to trace the error you should find the field, it should look something like this:
You can now just resolve this issue by filling in the field properly.