A letter to change a reservation

To whom it may concern,
I am writing to change the hotel reservation I made last Tuesday. I am Mr. Smith from ABC company.
The first thing I would like to change is its date. I originally reserved a meeting room for next Monday, but I would like to change it on to Tuesday the following day. That is on Tuesday. The second thing I want to change is the meeting room size. A medium size on is not enough, I need a large one since there will be more customers.
Could I ask you about the availablity of room facilities? For example, do you equip rooms with overhead projectors or other alternatives. We do need one because there might be a presentation during our meeting.
I hope these changes would not bother you, and I would like to hear from you as soon as possible.
your Sincerely,
hitperson

General Notes:

--Anything you 'originally' did would be in the past tense, since it already happened.

--"on the following day" is certainly a common phrase in certain formats, but if you change something, you would change it 'to'.

--I've simplified the sentence as you don't necessarily need to establish the day of the week itself in a separate sentence if it is only a minor clarification. It could also be "the following day, Tuesday." or something similar, where you are listing it as an additional item in the same sentence.

--Last sentence of your first paragraph, you say that you want to change the room size, but you don't specify a minimum number of people. Normally room sizes are established based on the number of people, as all meeting halls can only house a maximum amount of people due to the number of tables or fire department regulations.

--'Customer' is a perfectly okay word, but in business letters, the more universal term is 'client'. Clients or clientele can describe a customer in <em>any</em> type of business.

--'Sincerely,' is the most common ending before a signature, but anything you do use must be capitalized.