I need to replace the following characters:

ă with a

â with a

î with i

ș with s

ț with t

The replacement must be case sensitive. For example if a letter is upper-case then it must be replaced with an upper-case letter. 

I've read that I could use `sed` for this process but I don't know how to use it. Can anyone help me by writing the exact command that I must run in Terminal?