The thing that's responsible for slowing down your Android phone is you.
All those apps and junk that you downloaded over the months and years are now kludging up your phone.
And once this junk is on your phone, it can be a real pain to weed it out.
Here's my solution.
Download and install CCleaner.
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I'm wary of "optimization" apps, so it's taken a bit of testing for me to feel that not only is CCleaner safe to run but that it also does help speed things up by freeing up RAM and sweeping away the detritus.
And CCleaner goes much deeper than deleting apps and cat photos. It wipes application caches, download folders, browser history, clipboard content, and more.
And talking about photos, CCleaner will help you there too. With a single click CCleaner can find and remove similar, old, and poor quality, use compression to optimize file storage, and even move your photos into the cloud.
CCleaner also speeds up your phone by freeing up RAM and stopping apps from running in the background so you have as much power at your disposal that your phone can find.
I've found CCleaner to be so useful that I've even paid for the pro version so it can automatically clean my phone on a schedule every few days.