You won't be able to overclock with that motherboard, & moving to a Coffee Lake CPU (i.e. the i5-8600K) means a brand-new motherboard on top of the CPU.
However, you don't need to worry about doing that. With the CPUs supported on your board (https://us.msi.com/Motherboard/support/B150-PC-MATE#support-cpu), you can easily replace that i3-6100 with an i5-6600 (non-K). Or, if you first update your BIOS to version 7971vCA, you can go for an i5-7600 (again non-K). There's no point in getting the "K" variant for just a few extra clock cycles, especially when you'd have to also pay for a CPU cooler (since they don't come with one). That would allow you to not only replace the CPU, but also let you spend money on the RAM as well.
Currently, the Kaby Lakes are slightly cheaper than the Skylakes, so this is what you can get:
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel - Core i5-7600 3.5GHz Quad-Core Processor (€194.90 @ Caseking)
Memory: G.Skill - Trident Z 16GB (2 x 8GB) DDR4-3000 Memory (€152.74 @ Amazon Deutschland)
Total: €347.64
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-03-16 13:51 CET+0100
Note that the G.Skill Trident Z kit was not only the cheapest option for DDR4 listed on PCPartPicker, but it's on the officially supported list for the motherboard (https://us.msi.com/Motherboard/support/B150-PC-MATE#support-mem-4). And that saves you the cost of having to buy a new motherboard (almost 100 euros) & the time to reinstall Windows.