Moving to a new theme implies re-doing all the changes you might have made on your older theme, on the freshly installed one, from scratch, since there is no way to combine the two themes, or to simply move your changes onto the new one.
Depending on how many of the functionalities you'd have to transfer/add to a new theme, we'd be able to assess them and provide you with an estimation of costs and time. Please provide us with some more details on what changes would you need exactly via chat or email at [email protected], and we'd be glad to assist you further.