Buy a better system
Buy a whole bew system ???
Can't i upgrade ????
You definitely need more RAM, a better CPU and more disks (or better still, a couple of SSDs) - and if you're using only integrated Intel HD Graphics, then you need a discrete later-generation nVidia GPU such as a GeForce GTX 1050. In fact, if you're not using a discrete GPU (graphics card), the integrated Intel graphics will steal a small portion of the installed system RAM for itself, making that percentage of the installed RAM completely unavailable to programs.
The latest release of Premiere Pro CC requires a minimum of 8 GB of RAM (16 GB or more recommended) just to even run at all. And your i3 CPU has only two physical cores and only four processing threads - and no dual-core CPU is as powerful as even a mediocre quad-core CPU that's two generations older than the given dual-core CPU. Finally, a single HDD for absolutely everything (OS, programs, pagefile, cache, projects, media and exports) will become absolutely strangled for throughput no matter what: With all the OS housekeeping going on on that same disk, you'd never attain a disk IO throughput that's better than an abysmal 32 MB/s - far below what the disk itself is capable of.
Unfortunately, memory prices are still high. 16 GB of DDR3-1600 RAM still costs more than $150 right now. And check your motherboard's manual to see if it can accept an i7-4790 CPU. Otherwise, if you bought that system pre-built with no manuals for the individual components, then you may need to buy a whole new system. As a matter of fact, you might as well buy a whole new system if the total cost of the upgrade components needed to bring that system's performance to par is over half the cost of a whole new midrange PC.
Lastly, you may need to update your system's OS to Windows 10: Windows 7 does not natively support AC-3 (Dolby Digital) audio, and the latest release of Premiere Pro CC now no longer has built-in AC-3 audio decoding or encoding support, and will now only use AC-3 decoding that's native to the OS.