If you wished to lock in that profit, you could do as smallfil posted, and sell-to-exit.
At that point, should the underlying fall, you have 100% of your current profit.
Should the underlying continue to climb, you don't participate.
Put slightly differently, if you owned the 340, you could sell it now, and realize a greater profit/harvest than if you waited. {$32 versus eventual $16}
As an alternative, you could sell an ATM option, and lock in the difference between your long and short position:
TSLA is at $356 right now.
TSLA Jul20 340 call is ~$32. ($16 extrinsic; $16 time value)
TSLA Jul20 355 call is ~$23.50 ($1.50 extrinsic; $22 time value)
If you sold the 355 against your owned 340, you would lock in $15 extrinsic net on expiration, you would also have an additional $22 in hand, from the time value of the sold ATM 355 call. {bringing in now $37}
This is what happens if TSLA doesn't move.
What happens if TSLA...
falls by $20??
falls by $10??
climbs by $10??
climbs by $20?!?
Graph this out. And then make your choice.