hi, alorsnon. welcome to chinaphonearena!
Just wanna note a couple of reminders: Most of the time, rooting could mean losing warranty with your seller. And however common rooting is, there is always a risk to fall into a messy situation -- so make sure you have a backup ready.
And for the actual answer to your question...
I read that Kingo root tool works on the Y100. You can download the tool from here
[Only registered and activated users can see links Click here to register]
Just install Kingo root tool on your PC, then connect your phone with a USB data cable.
(Don't forget to enable USB debugging on your phone.)
When the program recognizes your phone, click the root button. Wait until the process finishes.
Click on Finish to reboot your phone.
You should then have a SuperSU app. Run it and update binaries.
good luck!
Let us know if it works out
Oh, and if you need to make a backup, you may want to take a look at this
[Only registered and activated users can see links Click here to register]
The program is optimized for the newer SOCs -- MT6752 and 6732 are specified. Not sure about MT6735. You can try though, or you can ask on that thread if it will work for 6735. I'm sure simone will respond.