The hard part is over.
I'm matching you with one of our specialists who will be calling you in the next few minutes.
The reason being is Capital Gains Tax. If you inherit the house, when the time comes to sell the house, then the capital gains tax base will be the value of the house on the day that Dad passed.
If you change the Deed to joint ownership, when the time comes to sell the house, then the capital gains tax base goes all the way back to when your Dad had bought the house. If Dad had owned the house for many decades, there could be a hefty tax.
Also, if your name is placed on the Deed that could be considered a "gift", thus the IRS may have your Dad pay a Gift Tax.
Curious why you are so anxious about having the Deed changed. Are you thinking that maybe Dad didn't put into his Will that only you get the house?