It is very likely that someone else is using your unsecured network, causing slowdown. A password would be a good idea.
I’ll give you generic instructions, but knowing your router’s manufacturer and model # would really help.
First, in your URL bar, go to 192.168.1.1 (usually the default ip)
Next, type in whatever username and password. Default is “admin” for both
Next, go to the security tab.
Turn on either WEP,WPA, or WPA2.(that is in order from least to most secure)
Save, and change the setting on your laptop to connect.
Uninformed, incorrect answers should be kept to oneself.