Didnt you say you booked (not changeble) pre-paid rate?
As for the Thread on the Hilton Munich CITY, my experiences are totally different and a lot more recent. Also, from the description of some people I think they stayed at the Hilton Munich PARK, which is a lot nicer property, just a bit far away from the center.
Lots of rooms in the Hilton Munich CITY smell like ash-trays and/or sweat,... especially the chairs and couches, which also had lots of stains on them. Talking about stains, dont even get me started on the carpet,... and most important, DO NOT MOVE THE FURNITURE... you might be surprised what the carpet used to look like. The furniture itself is cheap and old. Overall the place needs serious refurbishments.
If you can cancel the reservation my advice would be to do so. If you dont like the Le Meridien, the "Sofitel Munich Bayerpost" is also very nice and central and should be a bit cheaper than LeMeridien. As said before, if you wanna experience something outstanding, spend a night at the Rocco Forte Charles Hotel,... one of Europes best hotels and one of the best Spas i've ever seen in my life. Costs around 250-300 EUR / night, but totally worth it,... the cosmetics/toiletries in your bathroom already have a value of around 60 EUR ("REN cosmetics" products).