Problems after wordpress version is 4.2.4

Firstly the current version is 4.3.

Secondly without a link to your website it is very hard to assist with speed issues.

Generally I would try disabling all plugins and testing the sites performance and then re-enabling your plugins one by one to see if any of them impact your performance.

Some “Premium” themes can also affect your performance if they have lots of features such as Page Builders and complicated options pages as they tend to load a lot more resources during page load both in the front end and admin dashboard.

The website is https://www.sunontherunspraytan.co.uk

Also when I try & update to 4.3 I get error coded 404 – Page not found

It looks like you have an error in your theme and loading Javascript.

If you use a commercial theme or plugin and need support, please go to their official support channel. In order to be good stewards of the WordPress community, and encourage innovation and progress, we feel it’s important to direct people to those official locations.

https://themeforest.net/item/bridge-creative-multipurpose-wordpress-theme/7315054

Forum volunteers are also not given access to commercial products, so they would not know why your commercial theme or plugin is not working properly. This is one other reason why volunteers forward you to the commercial product’s vendors. The vendors are responsible for supporting their commercial product.

Thanks, I will go back to the developer then. Hopefully he can shed some light on it.

I’ve just noticed this within admin
ray() expects parameter 1 to be a valid callback, function ‘wp_site_icon’ not found or invalid function name in /home/sunonthe/public_html/wp-includes/plugin.php on line 496