Visual Studio replace tab with 4 spaces?

First set in the following path Tools->Options->Text Editor->All Languages->Tabs if still didn't work modify as mentioned below Go to Edit->Advanced->Set Indentation ->Spaces

You can edit this behavior in:

Tools->Options->Text Editor->All Languages->Tabs

Change Tab to use "Insert Spaces" instead of "Keep Tabs".

Note you can also specify this per language if you wish to have different behavior in a specific language.