Android Download large files

I am very new to Android development and I am trying to upload a 25 to 50 MB file to a web server and I am getting an out of memory error. I have been scared for the last 2 days and have no idea where I am going wrong.

Are there any suggestions as to where I am going wrong?

The code I am working on is

private FileInputStream fileInputStream = null;
private int bytesavailable,buffersize,bytesRead ;
byte buff[];
int maxBufferSize = 1*1024*1024;
String server_url ="server_url";
DataOutputStream dos;
String Builder response = new String Builder();
String body = "boundary values";
String body2 = "Boundary values";
URL url = null;
    try 
    {
        url = new URL(server_url);
    } 
    catch (MalformedURLException e1) 
    {
        e1.printStackTrace();
    }

    HttpURLConnection conn = null;
    try 
    {
        conn = (HttpURLConnection) url.openConnection();
    } 
    catch (IOException e) 
    {
        e.printStackTrace();
    }
    try 
    {
        conn.setRequestMethod("POST");
        conn.setDoInput(true);
        conn.setDoOutput(true);
        conn.setRequestProperty("Connection","Keep-Alive");
        conn.setRequestProperty("Content-Type","multipart/form-data; boundary=A300x");
        conn.connect();
        dos = new DataOutputStream(conn.getOutputStream());
        dos.writeBytes(body);
        File inputfile = new File(sourceFile);
        fileInputStream = new FileInputStream(inputfile);


        bytesavailable = fileInputStream.available();
        buffersize = Math.min(bytesavailable, maxBufferSize);
        buff = new byte[buffersize];
        bytesRead = fileInputStream.read(buff, 0, buffersize);


            while (bytesRead > 0) 
            {

                dos.write(buff, 0, buffersize);
                dos.flush();
                bytesavailable = fileInputStream.available();
                buffersize = Math.min(bytesavailable, maxBufferSize);
                bytesRead = fileInputStream.read(buff, 0, buffersize);
            }
        fileInputStream.close();
        dos.write("\r\n".getBytes());
        dos.write(body2.getBytes());
        dos.flush();
        dos.close();
} 
    catch (ProtocolException e) 
    {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    int iresponse = 0;
    try 
    {
        iresponse = conn.getResponseCode();
    } 
    catch (IOException e) 
    {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    //printStream(conn.getInputStream());

    if (iresponse == HttpURLConnection.HTTP_OK) 
    {

        BufferedReader input = null;
        try 
        {
            input = new BufferedReader(new InputStreamReader(conn.getInputStream()), 8192);
        } 
        catch (IOException e1) 
        {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

        String line = null;
        try 
        {
            while ((line = input.readLine()) != null)
                response.append(line);
        } 
        catch (IOException e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        try 
        {
            input.close();
        } 
        catch (IOException e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }


    return response.toString();