Create an ETC wallet
https://classicetherwallet.com/it's similar to what you are already using,
https://www.myetherwallet.com/next calculate how much ETC you want to convert
if by split you mean an even-split (half split or 50%), then
open a calculator and enter the total amount of your ETH (let's say you have 5.48847420417124 ETH) and multiply that by 0.5
(5.48847420417124 * 0.5) = 2.74423710208562 (that's half of your ETH)
in other words
(your Ether * zero point five) = half of your Ether
exchange that amount to ETC (you can use shapeshift.io)