you can use any version you like, but .21 has some new features that you may take advantage of. Like UPnP for example. To update first backup your wallet
. Then download the binary or source from bitcoin.org
, unistall the previous version and install the new one. Thats it. If something goes wrong you'll still have your backup wallet and will be able to restore your coins.
Regarding unconfirmed coins, it may be due to several reasons:
1. Like Hawkix
said, you need to wait for six blocks to be generated.
2. If it was a low amount and you did not include a fee it may be delayed, because we have more and more transactions and priority is given to big, old and paid for transactions
If you download new version and turn on UPnP, your node will be better connected with the network and you should see more than 8 connections. This should help the process too