Introducing regular formula?

Br

So my daughters been on EleCare since she was four months old and now she’s eight months and seems to be doing really good. She’s had some really bad stomach issues in the past and this is the only formula that has been working for her. I have introduced dairy through food and she seems fine so I’m wondering if it’s OK if I can start her on regular formula? I just don’t know how to go about it… Should I mix it in with this formula or do I do half of her bottles with regular? Does anybody have any experience with this? Thanks! (The reason I want to switch her is so it’s easier to switch her to milk when she’s one and we’re also paying $600 a month through insurance for elecare and it’s a lot especially right now)