You shouldn’t just delete the old bike entry — that would erase your sales history and could cause issues if you need proof later.
Instead, you normally do it in two steps:
Record the sale of the old bike
Note the sale date, price, and buyer (if relevant).
This ensures your asset register or personal records show it was disposed of.
Record the purchase of the new bike
That way, your records clearly show both transactions — one asset going out, and a new one coming in. The difference amount of the sale/purchase (OLD) will go to gain/loss on disposal of asset.