How can I reinstall wifi on Macbook Pro?

It wasn't a wireless card, rather I believe the IP was referring to reinstalling software. By Intermittent I mean that most of the time I cannot connect to the Internet ... but occasionally it will connect briefly. The wifi modem is provided by the Internet Provider but has been replaced twice in the last week. In six years with this computer I never had a problem. Recently, about when the problems began, I shifted telephone service to this IP. The things we've tried over the past few days are so numerous and out of my league that there's no way I can list them. In monitoring performance, a sample of the results is shown below. There are 16 to 18 other networks in the vicinity and this could be a contributing factor to the poor quality. As well, the age (in computer years :-) of the laptop could be a factor.

Thank you Jimmy for your response. It was helpful in that it was something not tried before but I did all this twice and it didn't work. I honestly think the problem is with my internet provider but they have spent hours with me on the phone and in my home and are stumped. Their own equipment had no problem connecting to Wifi with the modem, which is why they thought it was my laptop at fault.

Thank you for taking the time to reply - but that's not really the issue. I have a desktop Mac and there's no problem with the Internet. The Mac laptop is portable and needs to be able to receive wifi elsewhere, in and outside the house.