B3 and kB3 (1000 B3) are the same coins, only coinexchange has created two separate wallets for their markets. So if you want to trade on coinexchange then you need to move your coins from the B3 wallet to the kB3 wallet, if you want to move your coins somewhere else, like to a desktop wallet, then you can move them there right away. However, it is not clear what coinexchange will do once they discontinue their B3 market but you will need to move your coins from there anyway.