I just graduated in an engineering discipline.
First year is not a huge jump in terms of difficulty. As someone mentioned, your first year will mostly include A-Level maths and A-Level physics content and you will probably have seen most of the first year content in your A-Levels. I remember sitting my formative engineering exam in my first year and literally the whole exam included just A-Level physics questions about EMF, gas dynamics (internal energy, work done and heat transfer), kinetic and potential energies and statics (calculating reaction forces, centres of mass etc.). Obviously, this would depend on what engineering subject you're studying. I studied Aerospace, so a lot of my content included fluid mechanics and gas dynamics, however if you study electrical engineering then it will involve more electronics stuff like ohm's law etc. However, you can mostly just expect A-Level stuff in your first year. My first year maths module was all just A-Level maths and A-Level further maths. You will likely review topics such as trigonometry, vectors, differentiation, integration, complex numbers and matrices etc. Easy stuff.
In your second and third years the difficulty will increase a bit. In my second year, I studied maths modules and topics that I was unfamiliar with. In particular Laplace transforms and Fourier series. It can be a bit difficult to get your head around these topics, but take things slow and always ask for help. One thing that has really helped me in second and third years is getting the reading material required for each module. So for example, in every module, the lecturers will tell you what books you should use throughout your studies. I suggest that you don't rely too much on the lecture content and try to get yourself some of these textbooks and go through them in your own time. I had exams where the lecturers haven't covered certain material in lectures but the content was covered in the book, so having a textbook that covers all the content really helps and it really enhances your understanding.