How to switch user in terminal

You should use su:

su [-|-l|--login] USERNAME

If you specify the login option (either -, or -l, or --login: all are synonyms), you will get an environment similar to if you directly logged in as that user. Otherwise you stay in the current environment (e.g. many env variables, the current directory, etc).

Example: (note the usernames and current working directories!)

root@wolf-pack:~# su bytecommander
bytecommander@wolf-pack:/root$ exit
exit

root@wolf-pack:~# su - bytecommander
bytecommander@wolf-pack:~$ exit
logout

root@wolf-pack:~# 

PS: If you run su not as root, you will of course be prompted for the password of the user as who you want to log in.