I've hacked Windows passwords lots of times (after buying computers dirt cheap at auction and then finding that they're password protected). It's not a particularly complex process but it might be a little daunting for someone who's not technically minded,
First, on the locked machine, you need to go into the BIOS to check that the first place that the machine will look for a boot-up file is either a CD or a USB memory stick (depending upon what you're planning to use). Confusingly here, you often need to tell the machine to look for a hard drive when you want it to boot from a USB drive.
Then, on a different machine, you need to download and burn the ophcrack LiveCD. (Note that the LiveCD only works up to Windows 7. For Windows 8 and 10 things get a bit more complicated, requiring to handle an ISO file. Also note that, despite its name, a LiveCD doesn't have to be a CD; it can also be a memory stick).
http://ophcrack.sourceforge.net/
Then insert the CD/USB stick into the locked machine. Turning it on will then result in the machine booting from the LiveCD, which contains its own operating system. It will automatically seek out all login data on the hard drive.
If that's a bit complicated for you, any decent computer technician should be able to do the job. (Shop around though. PC World will charge you fifty quid for what will, if they've already got the LiveCD to hand, be only a few minutes work).
[NB: I've assumed that it's a Windows password that's required, rather than a BIOS one, as very few people lock the BIOS on their machines. To remove a BIOS password you have to open up the machine and disconnect the CMOS battery]