In order to answer this question you first need to understand lumens (XLM). Why the Stellar network needs them and what role they play.
You can learn more about this on the Stellar website, but below is a list of operations on the network which require lumens.
So it follows, that if your lumens are being used for any of the operations below, then you will not be able to transfer them out of the wallet.
All accounts on the Stellar network require a minimum balance of 0.5 lumens, the base reserve.
The minimum balance for a DMC android wallet is 2 x the base reserve = 1 lumen.
EACH ADDITIONAL ENTRY COSTS THE BASE RESERVE.
In order to add an asset to your wallet, you are establishing a trustline. So for each asset you add to your wallet, 0.5 lumens are encumbered.
This is not applicable to the DMC wallet, but with multi signature wallets, every signer requires an additional 0.5 lumens.
For each trade you post, 0.5 lumens are encumbered.
Posted for trade
Check if you have any open trades. If you have posted a trade, then you cannot transfer out the assets offered for sale.
The base fee, currently 100 stroops (0.00001 XLM) is used in transaction fees. The fee for a transaction is:
# of operations x the base fee.
The DCM android wallet currently does not have a merge function, so you cannot merge your account with another wallet address and transferred out the base reserve. This feature is on our development roadmap and will be introduced in the coming months.
The DéMars team have added 5 lumens to each wallet to encourage Users to add lots of assets, exchange and transact with them. Without worrying if they have enough lumens to cover transaction fees.
If you are considering transferring out the lumens you received on account activation, why not try and add other assets to your account, like Bitcoin (BTC), various currencies, STOs etc. There really is no need to trade via an exchange as we can retain complete control over your private keys and trade assets at almost no cost within the wallet.
You can view the most liquid and traded assets on the Stellar Expert network explorer.