Net Worth Beginning is the net amount from the beginning balances from all the Assets less all the Liability and other Equity accounts.So in order to change the Net Worth Beginning amount, set up an equity account and put a beginning balance in it, or adjust the beginning balance for some other account.
When this amount is zero then it will not appear on the balance sheet.
If there is an amount in the Prior Year's Net Income, then this amount can be adjusted by selecting Accounts | Equity Name Changes. By zeroing this amount it will not appear on the balance sheet.