As per:
https://www.arctic.ac/worldwide_en/p12.html
They're 3pin connectors - so will connect to your motherboard fan headers.
Checking your manual here:
https://www.asus.com/Motherboards/H81PLUS/HelpDesk_Manual/
Page 11/74
You only have 1x CPU Fan header (near the CPU) and 1x Chassis Fan header (to the left of the CMOS/Round silver battery) on that board - So you're going to need a splitter, or a controller.
I can't tell what fan ships with that case, whether it uses a motherboard header or if connected to the PSU.
If the existing fan is connected to the PSU, you have a free fan header (Chassis Fan) and a single 3 way fan splitter will be fine:
Something like this:
https://www.amazon.ca/Cable-Matters...ter+3+pin&qid=1575055743&s=electronics&sr=1-3
That's a 2-pack, just incase you need it.
Most headers can provide up to 1A, and each of the Arctic fans are 0.2A.
If the existing fan is not connected to the PSU, and is currently connected to the Chassis_Fan header on the motherboard, you're going to need another splitter - or a controller.
Controller example:
https://www.amazon.ca/KingWin-Multi-Fan-Controller-Individual-FPX-005/dp/B00DP9WRZY/ref=sr_1_14?keywords=fan+controller&qid=1575055645&s=electronics&sr=1-14&th=1
Or you could do the 3way splitter as above, and a 2way splitter from your CPU_fan header (so the existing 'included' fan and the CPU fan will run at the same speed/power) - you could use the 3way splitter as part of the 2pack I listed above, or a similar 2way splitter which you'll find via a quick Google search or Amazon, Newegg etc.