upgrade from wheezy to jessie

[Gerard ROBIN <g.robin3@free.fr>]

Hello,
usually when the distribution changes, I update my system rather than 
reinstall everything. But for the transition from wheezy to jessie, 
I would like to know:

-1- Is it possible to go from wheezy to jessie, keeping sysvinit.

-2- if not, from what I read on the internet, go from sysvinit to
    systemd is not without risk. What about it exactly?

(I would say that I am not concerned whether sytemd is better or 
worse than sysvinit. I'm not proficient enough ...)

tia.

-- 
Gerard
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