Trying to upgrade well everything on my HP p6774y

Hello,
my computer is a few years old now and since i bought some cool stuff to add to it (tv tuner and a blu-ray burner) i thought now was as good a time as any to upgrade. i have AMD Phenom II x4840T Quad Processor 2.90 Ghz with 6 GB DDR3 system memory, ATI Radeon HD 4200 integrated graphics, 6 GB installed memory with 5.75 GB available. I want a lightning fast computer and internet capabilities. i play online games but im not a die-hard gamer. i stream movies, tv shows, music and videos online. i hope this information is what is needed to answer my question and pls forgive me if i used any of these tech terms improperly. im not a comptr guru, infact "computers for dummies" is way outta my league!