Comparing to the newest Android smartphones, iPhone 4 is nothing but old premium flagship of Apple. It runs perfectly smooth in iOS 5 but snail-like in iOS 7.1.2 even when you're using it to access internet. Nevertheless, iPhone 4 still looks cool and premium which honestly I decided to buy it. It works perfect and reliable for daily use but installing latest apps that require above iOS 7.1.2.
iPhone 4 is basically powered by 500MB only. You should install old apps that you really need or just a number of apps to save some iPhone 4 RAM resources. Multimedia data you store in your iPhone 4 don't really matter. No need to delete it.
Also Read: Is iPhone 4 Obsolete?
Another good method to make your iPhone 4 faster is jailbreaking it to completely remove useless built-in apps like Stocks, Weather, Game Center, and Passbook. Furthermore, you may install tweaks from Cydia to boost your iPhone 4 faster. I highly recommend installling Nitrous, Pwntunes, Speed Intensifier, and Notification Killer.You don't have to be a tech savvy to jailbreak iPhone, which is easy as pie. Install Pangu for iPhone 4 iOS 7.1.2 and follow the instructions to start jailbreaking your iPhone 4.