Unable to install npm in Ubuntu 16.04

Question

I have installed nodejs

$ nodejs -v 
4.2.6

now i am trying to install npm i tried

sudo apt install aptitude

sudo aptitude install npm

it is showing

/usr/local/bin/node: 1: /usr/local/bin/node: cannot create 8��@P_�@@$@@@@@��@@@@�"��"� �"��"�'���
                                                    H&�H&'H&'00@@DDP�td �� �� ��ttQ�td/lib64/ld-linux-x86-64.so.2GNUGNU
                 eØGcP?ֺ����x��)Ě��@�: Directory nonexistent
/usr/local/bin/node: 1: /usr/local/bin/node: ELF: not found
/usr/local/bin/node: 2: /usr/local/bin/node: 3�
                                               : not found
/usr/local/bin/node: 3: /usr/local/bin/node: Syntax error: ")" unexpected

How to install npm