Run uninstall before installing. Removes old files. Still need version checker and deleting pyc/pyo files

scripts/pyfa-setup.iss

@@ -105,4 +105,45 @@ begin
     begin
       Result := '';
     end
-end;
+end;
+
+function GetUninstallString: string;
+var
+  sUnInstPath: string;
+  sUnInstallString: String;
+begin
+  Result := '';
+  sUnInstPath := ExpandConstant('Software\Microsoft\Windows\CurrentVersion\Uninstall\{{3DA39096-C08D-49CD-90E0-1D177F32C8AA}_is1'); //Your App GUID/ID
+  sUnInstallString := '';
+  if not RegQueryStringValue(HKLM, sUnInstPath, 'UninstallString', sUnInstallString) then
+    RegQueryStringValue(HKCU, sUnInstPath, 'UninstallString', sUnInstallString);
+  Result := sUnInstallString;
+end;
+
+function IsUpgrade: Boolean;
+begin
+  Result := (GetUninstallString() <> '');
+end;
+
+function InitializeSetup: Boolean;
+var
+  V: Integer;
+  iResultCode: Integer;
+  sUnInstallString: string;
+begin
+  Result := True; // in case when no previous version is found
+  if RegValueExists(HKEY_LOCAL_MACHINE,'Software\Microsoft\Windows\CurrentVersion\Uninstall\{3DA39096-C08D-49CD-90E0-1D177F32C8AA}_is1', 'UninstallString') then  //Your App GUID/ID
+  begin
+    V := MsgBox(ExpandConstant('An old version of pyfa was detected. Due to recent changes in the application structure, you must uninstall the previous version first. Do you want to uninstall it?'), mbInformation, MB_YESNO); //Custom Message if App installed
+    if V = IDYES then
+    begin
+      sUnInstallString := GetUninstallString();
+      sUnInstallString :=  RemoveQuotes(sUnInstallString);
+      Exec(ExpandConstant(sUnInstallString), '', '', SW_SHOW, ewWaitUntilTerminated, iResultCode);
+      Result := True; //if you want to proceed after uninstall
+                //Exit; //if you want to quit after uninstall
+    end
+    else
+      Result := False; //when older version present and not uninstalled
+  end;
+end;