I deleted the categories so I could start again making new categories because it was wrong but then it deleted all the transactions and all the work I've done

Hello harry_ray

Thanks for joining the Community. 

You can recover the transactions by re-activating the chart of account (category) - to do this, click the settings wheel > chart of accounts > select the small gear > tick 'include inactive' > select 'make active' beside the account. 

You can then merge the account containing the transactions with the new account (category) by editing the details (please note, accounts with online banking can't be merged). The account type, detail type, and name should be changed to match the account you want to keep exactly - when you're ready, select Save and then Yes on the pop-up to confirm.