Hi Katie, when dealing with SpeedCheck adware first you must uninstall it using Control Panel (this adware is known to use several names, for example "SpeedCheck", "SpeedChecker", "CheckMeUp", "SpeeditUp", "IneedSpeed", "InterStat" and several other). When in Control Panel be sure to double check if none of the mentioned applications are present in your computer. After uninstalling any suspicious applications using Control Panel follow this removal guide and eliminate any related plug-ins from your Internet browsers (https://www.pcrisk.com/removal-guides/8278-ads-by-speedchecker).

If after performing these steps you still see "Ads by SpeedCheck" when browsing the Internet scan your computer with Malwarebytes Antimalware (https://www.pcrisk.com/top-spyware-removers) and AdwCleaner (https://toolslib.net/downloads/viewdownload/1-adwcleaner/). After this procedure your computer should be adware free - let me know if this helped.