As NEO is not divisible and can only be withdrawn in whole numbers, you will have to convert to GAS to withdraw your funds.
Under the Trading Pairs dropdown, select the GAS/NEO trading pair.
The order book will reflect multiple sell orders of GAS where you can:
- Buy GAS with your fractional NEO to obtain more GAS
- Sell GAS and obtain NEO to convert your fractional NEO into a whole number