You can uninstall Paste the same way as any other app on your Mac:
- Quit Paste first by right-clicking on the P icon in the main menu bar
- Remove the app as described at https://support.apple.com/en-us/HT202235.
On iPhone and iPad
- Touch and hold Paste's icon.
- Select the "Remove App" item from the context menu.
- Tap Delete App, then tap Delete to confirm.
Please note that when you delete Paste on your iOS device all its local data will also be deleted on that device. You can download it from iCloud if you install it in the future.
Delete Paste's data from your iCloud
If iCloud sync turned on, Paste stores a copy of your data in your iCloud account. You can delete it at any time in System Preferences → Apple ID → iCloud → Manage (right bottom corner, next to the available space indicator) → Delete Documents and Data.