Simple, in your wallet click settings then a window will pop up. Then click the display tab and check the box that says "Display coin control features" Once done click apply and OK. Now to split them into 2.5k blocks you need to send coins to yourself so click on send coins, then you will see a tab "Inputs" click that, once done a pop up window will show and then you need to click "list mode" now you will see all your coins in your case your 5k block. Now check the box next to that 5k coins, then click OK. Now in the Pay To enter your wallet address and in the amount box enter 2.5k and don't forget the 0.10 Rain fee so it will be 2500.1 and then click send. That is it now you have your coins split into 2.5k blocks.