I wouldn't replace that HEPA Filter quite yet. Assuming the seller replaced it on a yearly basis, it's likely 1 year old or less. Those Miele HEPA Filters can go at least 2 years, sometimes 3, before they need replacement. Most people don't realize the cloth bags are capturing the fine dust for the most part, only carbon dust and ultra fine particles you can't see is what makes it to the filter.
If you want to replace the HEPA Filter because it's smelly, try spraying it with Febreze a couple times and let it dry in between sprays. That ought to rid the filter of the odours. Another thing you could try is putting baking soda on the underside of the filter and let it sit for a few days on a sunny window ledge. Then take it outside with a vacuum with a blower and gently blow out the baking soda. It along with the sun should absorb any odours and help to renew the filter a bit.
Also, beware that the brushroll is VERY PRICY when it wears down and needs replacement - at least $100. So it might not hurt to find a nice used one to keep as a spare. Good luck with your Miele, hopefully you get many years of service from it.