Warning Don't download "Registry Booster" if you were asked to! I did & I want to delete it but Can't!?

I wanted to open an email but was asked to down load this: Registry booster programme Free of charge to be able to see the email, so I - regretfully - did! soon after I got Warning message that this programme caused 132 errors in my computer and now it might crash unless I download some other programmes costing.??..$ $ !! I tried to delete " Register booster" But I can't! What can I do? and how can I report these thieves?