There is currently no facility within mAnagr.com to transfer players from one squad to another. We did consider offering such a function but decided against it due to data protection issues - passing around the personal data of minors is fraught with moral, ethical and legal dangers.
If players are transferred, the manager of their new team needs to key in the details of that player even though mAnagr.com already has those details stored against their previous squad.
Be aware that you can mark players that are being transferred from your squad as having left by hitting the Player tab, followed by the Career tab and entering a Left Date. This will ensure that their history is maintained against your squad whilst not offering them for team selection in the future.