What do I need to do to speed up my computer, I had a computer guy out who did something, which made no difference at all, only the £40 to my purse. What is it that speeds up the computer?

It depends why it might be running slowly.

If it is slow due to lack of system resources then you might need more disk space, RAM or a faster CPU.

If there is running more slowly than it should be for its spec, you should try a good set of malware removal tools such as Malwarebytes Anti-malware.