You can upgrade your existing house with a home improvement loan given by a bank. Since you have bad credit, it could be little difficult for you to get a home improvement loan. However, you can find a lender who would offer you a loan. But the rate of interest could be slightly higher than you expected as you have a bad credit.
Otherwise, you can analyse the reasons for your bad credit and fix the issues at the earliest. Once your credit score is updated, you can apply for a home improvement loan to get the best offers.