Hi Kaviraj,
Welcome to our forum and thanks for contacting us with your question!
1. To make sure that you can upgrade your Highcharts, please contact our sales team. They will check if you license allows you to do it:
https://www.highcharts.com/blog/contact/
2. It depends what features do you use exactly. Most of the options, even if deprecated, should work without any problems. What might potentialy fail are custom plugins or function wraps. If you don't use them then you don't need to worry tho. If you have any particular features that you are worried about feel free to ask and I will check if the upgrade could affect them. Additionaly, you can take a look at our Changelog to see what exactly has changed since 4.2.7:
https://www.highcharts.com/blog/changelog/
You can also use our CDN to check if your charts would work fine. To do that, change version in the URL:
Let me know if you have any further questions!
Regards!