Hmm, it's definitely worth deleting any unwanted files, or moving them to an external drive or USB sticks if you can. Try to free up at least 10% of your total hard drive space.
If your machine has suddenly started to run more slowly, a vigorous sweep with your anti-malware program/s would be in order ? a complete scan, not a quick scan, and back this up with Malwarebytes or similar if you do suspect malware.
But if it's slowly ground to a halt, then the previous suggestions are the first steps to take.
Take a look at what's running at startup, as the previous poster suggested. Perhaps try Winpatrol for this (free). You can disable a number of things at startup, and delay others with this tool. BUT take your time, and do some research, so you only disable things you are absolutely certain you don't need. Used carefully, a startup control manager can stop a lot of unnecessary processes running (eg quick launch for applications you rarely use).
Finally. If feeling really brave go to www.crucial.com/uk and see if you can fit any more RAM into your laptop! Run their scanner program to find out, or find your model there.
If you choose to do this, it's fair to say that upgrading RAM is ridiculously easy, a 5 minute job at most.
As it's an Acer you might only be able to access one of two memory slots, but a modest RAM upgrade would still make a huge difference.