From your post I am assuming that you are Planning to take admission in engineering and not able to decide which branch to choose or you have already taken admission in Mech. Branch and now somebody suggested that Mech is very tough branch so you are scared .
As far as choosing a branch in engineering is concerned its more about your interest and what you want to do after getting your engineering degree.If your ultimate aim is doing MBA after engineering then Engineering branch plays a trivial role except in some cases.
But if you want to do a job right after your engineering then you should consider the kind of work you feel interested to.Whether you are fascinated by machines like turbines,cars etc. or you feel good sitting and coding in front of computer/laptops in Ac offices.
Being a Mech. Engineer you always have oppurtunities to work in different Industrial sectors like automobiles,Steel and Cement etc.
If any time of life you feel that IT sector is better you can always shift to IT sector as a Consultant/Project manager/Analyst but that depends on your experience.Even as a Mech Engineering fresher you can join IT companies(if by the end of engineering you started feeling like IT is better).
If you are good at understanding basic concepts and applying them practically than Mech is definitely a good branch.
regarding the semester studies and all there may be some subjects in Mech branch like heat and mass transfer, RAC, thermodynamics which some people consider as tough but at last guys belonging to any branch have to study the same number of subjects per semester and have the same time to study.
I just replied to your post so you can have some more ideas but this post is just for informational purpose don't take desicions based solely on this post consult your friends/relatives.And the fact is nobody can take decision on your behalf it's ultimately you who has to decide about your future.