Both live in Settings → Account, under Your project data.
Taking a copy
Press Export project data. You get a zip containing your items as a spreadsheet, plus your uploaded documents and receipts.
The download link works for seven days and the copy is then deleted. That is deliberate: an export is a complete second copy of your project sitting behind a link, so it should not be a permanent one. Anyone with the link can open it — treat it like the data itself.
Deleting a project
The Danger zone below the export removes the project: every item, document, category, room, payer and uploaded file. Everyone you invited loses access. It cannot be undone, and you type the project's name to confirm.
Any subscription on the project is cancelled first.
One thing is deliberately kept: the record that a payment was made. That is an accounting obligation rather than renovation data, and it holds no items, prices, documents or files. The Privacy Policy says what it contains.
Deleting your whole account
Also in Settings → Account. It removes your profile, your memberships, and every project you own — with the same retained payment records, and the same warning that it cannot be undone. Projects you were merely invited to are not affected; you simply stop being a member of them.
If you want a copy of anything, export it before you start. Once the deletion runs there is nothing left to export from.