How to add mobile Thunderbird and not lose messages on desktop version.

I've been a longtime Thunderbird user on my desktop (laptop actually). I'm wanting to start using Thunderbird on my Android phone. What I understand so far is that both the desktop and mobile have to have the same settings if I want to be able to send/receive (and have records) on both setups. I also understand that I need use IMAP settings. In my situation, I believe I set up my desktop to be POP but to leave messages on server until I deleted. So, my questions are these: Do I need to delete my POP accounts on my desktop first before adding the IMAP version of the account? If not, I can simply add the new account along side and then delete the old account. If I do need to delete the account, does deleting the account delete the emails as well? And how do I transfer any emails or sent emails from the POP to the IMAP? In as much as I have several accounts to transfer, I want to make sure my step-by-step works well for one then I can proceed to all the rest. Thx BobbyG:)