Issues with my Macbook Pro?

So a couple of weeks back my antivirus was going to expire and my dad was going to put a new one in for me. I went to work then came back for him to tell me it took him two hour to do it. So kind of thought well he doesn't really know how to use a Mac as he is a PC person. Going on and helped him, i did notice it was slow but shrugged it off as it just downloading the new anti virus.
Sadly the next day when i turned my mac on i noticed it was going rather slow. It started up screen appeared then my icon. I try to click my safari but it wasn't letting me. It was still loading itself. It took about nearly an hour or more for it to finally let me go on the web. Trying to click on my folders that also took ages! I thought that it needed an upgrade. Which i did and now its the OSX now but still so slow. I have like only used 90gb on my 499gb mac. So it wasn't that then thought maybe a virus did a scan and nothing. I really hope it isn't a ram 😟

My other issue is my old antivirus. Deleted the app for it but it keeps comign up telling me i need to renew it but i deleted it? It appears at the top of my screen which is really annoying. It keeps popping up and tell me its did a scan but also i need to renew it. So how i am able to delete?