Just write down this litte trick for further use. The problem how to replace one character in vim does be really simple for me now.

• First go into the Command Mode where you can issue many vi(m) commands.
• Move the cursor to the positon where your wanted character lies.
• Then press Key r (in lowser case) and enter your desired character to replace the wanted one.

Others

• ​​vi and Vim Editors Pocket Reference: Support for every text editing task​​