The most common wireless problem I encounter is poor access point placement. Wireless access points should be placed as high as possible, such as on a bookshelf, and away from sources of interference like speakers and landline phones.
Building construction is also a factor. Try moving your computer in relation to the access point. If possible, line-of-sight gives best performance.
If you have an older wireless router, consider replacing it. The newer devices have improved speeds and are better at resisting interference. Similarly, older computers will be slower on wireless networks.
Make sure it’s a wireless problem and not an overall network problem. If you’re still experiencing slowness when you plug in your computer manually, it’s not just the wireless. Try rebooting your router and/or modem according to your Internet provider’s instructions. Using a surge protector will prevent equipment damage due to brownouts or blackouts.
If there is a virus infestation on your network, this can also cause a slowdown as the virus tries to call home to its command servers. Run antivirus scans on all computers, and be especially wary of ransomware.