[digitalapnea]

Depends on what you mean by "manage". The money is explicitly yours, the company can never touch it. However; you are locked into the company agreement with the custodian (e.g. Vanguard and their list of investment funds).

[xgl5k]

Not locked. You can roll it over into a IRA/ roth IRA and manage yourself. You won't pay early withdrawal taxes as long as you roll over within 60 days.

[lotsofpulp]

An 401k custodian that allows an in service distribution (rollover while employed) is rare, and I think it is not even allowed by law before age 59.5.

Rollovers typically only happen after employment has ended.

https://www.investopedia.com/terms/i/inservicewithdrawal.asp