Hello how can i update my them without breaking my website

Hello my website is www.campervoet.nl and i cannot update my theme says my website programmer.
It has some custum coding on it.
Im currently on v7.4.1 | Unregistered but i want to know what to do tho get the newest version. Without breaking the website as it’s my form of income.


Contact with your purchase item author hope they will helped!