Can I change my gmail address without starting a new account?

For most people it's still no, a @gmail.com address is fixed. Google has been rolling out an option to change it on some accounts though, so check first: Google Account > Personal info > Email > Google Account email. If there's an edit option there, you can change it and keep everything. If not, the usual way is a new account, then forward mail from the old one and use Google Takeout or partner sharing for the photos. Keep the old account alive though, because things are probably still linked to it.