what type of case you think it will fit?Looking at pictures of the motherboard is appears to be a proprietary design so no.
https://drive.google.com/file/d/1DpbHyWE6CeDO8rh-QxU3_GTTg9Y438ZP/view?usp=sharing here's the link to my mother board pictureNone. The problem with most prebuilts is that they use proprietary motherboards and PSUs that fit on the cases they are designed for.
one more question i have i3 7100 processor in it can i take it to my new motherboard if ever ?? and also the heatsink? can i take thoseYes and that little part of the motherboard at the top right where it notches out, that's not standard. These computers are meant for Office environments with no upgrades in mind, just replacement. If you really want a new case go find yourself a cheap used/new B250 motherboard. Then buy yourself a half way decent power supply ( heres a list of good models and brands https://linustechtips.com/main/topic/1045610-new-psu-tier-list/ ) if you do plan on putting a graphics card in it.