Changing a character in a string

[Livne_ye]

Hello fellas! first time here.
i have the following string:
"ATCGATCGATCGATCGACTGACTAGTCATAGCTATGCATGTAGCTACTCGATCGATCGATCGACGATCGATATCGATGCATCGACTACTAT"

i want to write a command which will replace all of the "T" characters into "U" characters, and which the new "U" characters will be in the exact same location as the old "T" characters were.

like so:

"AUCGAUCGAUCGAUCGACUGACUAGUCAUAGCUAUGCAUGUAGCUACUCGAUCGAUCGAUCGACGAUCGAUAUCGAUGCAUCGACUACUAU"

do you have any idea how can i write such a command?

Thanks and have a great day