It would have only become possible to move to a segwit address in about late August 2017... so any coins that have not been moved before that would be in legacy addresses by default. There has been no automatic conversion to segwit addresses of legacy addresses (and I am not sure if such automatic conversion/movement would be possible).
No you cannot convert a legacy address to a segwit address. The addresses that start with a 1 can only be spent with the Pay to public key hash protocol. You also cannot covert a legacy multisig address to a segwit address, even though they both can use the pay to script hash protocol. The script hash used in legacy multisig is generated from a different redeem script than a segwit address. I am not quite sure how the new Bech addresses exactly work. But they use a totally different protocol as well and can only be used for segwit.