first of all you are suggested to visit a dentist
and take an OPG(XRAY).
in this you can exactly see the condition of your permanent teeth
,that means there path of eruption(lingual,labial,palatalor any other routes),amount of bone covering it.
your dentist can judge and tell approximately when it can come in oral cavity.
then, after confirming the position of your permanent teeth UNDERLYING you can plan and get your over RETAINED decidious (milk teeth)extracted.
also if your dentist, after analysing says, it will come in different direction even then you donot have to worry because it can be further corrected by orthodontic tooth movement.
i hope i have given you complete picture of your milk as well as permanent teeth?
so now relax ,plan and visit your dentist and proceed accordingly.