IMHO, if you have the options to “delete” or “ignore” during boot-time scan and you don’t have a clue, it is best to ignore, in order to keep the PC bootable. Otherwise you might delete a vital file and end up with a non-running system.
This should then be followed by other measures of course, and I like to start of with Malwarebytes Antimalware, which is a great tool for removing malware if you really got hit by bad stuff. Most of the time, MBAM does the trick.
Avast is a great prevention software, however, like with any other AV software, some sneaky stuff may get past it so that another tool needs to be used. Sadly, there is no panacea for malware around.