which slot to install ram - Dell Vostro 15 (3510) | SSD & RAM Upgrades rama 888 slot

I wanted to upgrade my Pc Dell vostro 15 3568 to maximum ram supported and i wanted to know which ram to buy 2600mhz or 3200mhz ........Which one should I go for?

To install a mortice lock on a wooden gate, the installer would have to chisel out the slot to fit the lock inside which requires precision.

I have 2 RAM slots. I already had 1 GB installed on one of these slots. A few months before I installed a 1 GB RAM on another slot(I gave my CPU to the shop actually to install it) and it was working fine.