As all app purchases you make are associated with the account that you used to buy them, if you change accounts, you will normally have to buy them again. This is the same for all apps, not just ours.
If you still have access to your old account, it is possible to have two accounts on your device so you could still use your old account to access your apps.
If for some reason you have lost access to your old account, or have some other mitigating circumstances, please contact us and we might be able to help.