From Han Wiki
I've been using this phone over a year, and I have nothing but accolades for this phone. However, it has started to become sluggish, and while searching for a solution I've located some tips that may help with optimizing the system w/o installing an app to do this.
Wipe the cache partition
First, you reboot the phone in Recovery Mode and then choose Wipe Cache Partition option. This seems to require a bit of experience to do it well and with ease. After the Google screen when it starts to boot up, hold Power and Volume Down button together. By the way, as of now, the OS installed is Android 6.0.1 (aka Marshmallow). Four animating icons will appear and then go into Flash ROM screen. Here, use the Volume keys to choose Recovery Mode and perss the Power button. It will reboot once again, and when you see an Android robot in the middle of the screen press both Power and Volume Up button together for about 3 to 4 seconds, and then release only the Volume Up and you should get a menu where you can choose that Wipe Cache Partition option. Be careful with this, because you can lose some settings for some apps.
For example, on Android Pay, it seemed that first I had lost information for debit and credit cards I had in there. All of the store reward and membership cards came back after few minutes. However, this is a security feature built in to the app. I had to verify the CVC code in order to restore those cards.