Tying myself up in.....

.....knots at the moment.  Our lovely Apple computer (named Greasy Mac) being a bit aged (like me) is running very slow (also like me) but I'm always a bit scared to change these things.  It's making sure a new one will do what I want it to and the dreaded transferring everything to a new one.  I can work this one (to do what I need to) but am not 'literate' in the terminology.  I can be completely confused in seconds!!