i want to format my iphone

If you truly want to erase your iPhone and "start over", the easiest thing to do is to Settings > General and check out the various reset options that are available there. For example, you might consider choosing "Erase All Content and Settings" if you wanted to completely erase your iPhone.

Be sure to backup prior to doing anything just in case.

Keep in mind this could also be a battery issue too - this has been mentioned quite a bit lately. The iPhone 5s isn't exactly new these days.

Make a full backup of your iPhone, then restore it to factory settings and, at the end, set it up as new.

Follow this support guide:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

In this way, your iphone is as new. Test it for a while.

Then, If you want, you can restore data from your previously made backup:

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Regards

Giulio

Hardik46 wrote:

iPhone 5s iOS 11.2.3

my phone is getting slower and slower day by day

That happens to all of us with age.

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Oops... Idris, I'm sorry. I didn't see your reply in time.

Giulio

ProustGiulio wrote:

Oops... Idris, I'm sorry. I didn't see your reply in time.

Giulio

No worries! Your post had information mine didn't.