How do I restore system files to the orginal ones?

Hey guys! So basically I have a galaxy s3 . Android : 4.3 Jelly bean .. So the emojis were displayed in black and white so I wanted to make them colorful people said colorful emojis aren't for Android 4.3 Jellybean And I did something wrong I downloaded The fallback font.Xml And droidsans files and I put them in the system files (I think it removed the orginal ones) And I restarted my phone hoping for the best but I saw that the things were messed up now It doesn't even show me emojis and I can't touch the fonts in the settings because it crashes this means that It deleted some system files and replaced them with wrong ones (The ones that I downloaded) And i tried to delete the droid sans and fallback xml in the system> fonts and system> Etc And my phone just messed up so I put them in the system files again now I can't see any emojis while I use snapchat or other apps. Is there anyway that I can get back my system files to orginal ones and make my system file fresh again? Please help I did some research and I think u have to reflash your rom is there anyway other than foing that to fix it??

First, before you do anything else, do a full backup. (See Backing up an Android Device.)

Copy the backup to your PC. (Make a Backup folder, so you can put all the files in one easy-to-find place.)

Reflash the ROM. (See [Samsung] How to flash Stock ROM via ODIN.)

Once you have the phone working with the stock ROM, start restoring everything from your backup. (Do this when you have the day free - it's going to take quite a while to back up, reflash, then restore.)

Hey Rukbat thanks for the information!

Well I'm a little bit scared of installing the ROM by Odin As it can fail and brick my device

So there are some custom ROMs like CynogeneMod and other ones my questions are :

1. Will it restore my system file back to default ones (Reflash it)?

2. Can i install it through (i think it's called recovery mod?) I mean after you wiped data you just choose Install Zip and that's it . Can i install the ROM like that?

3. Can i turn back my old ROM After i installed the new ROM?

0. I've used Odin about 50 times to flash my phones - and it works every time.

1. Yes, the system files are part of the ROM.

2. No. There are some files you can install that way, but the entire ROM isn't one.

3. After you flash a ROM, there's no "old" one - the one you flashed replaces the old one. If you're trying to save data that you have on the phone, Backing up an Android Device should do it.

(BTW, the largest danger in flashing a ROM is dying of boredom, so do it when there's a good TV show on. And see [Samsung] How to flash Stock ROM via ODIN for full instructions.)

Ok Thank you so much.
I also found something called 'UOT Kitchen' can i restore the fonts file (in the system file) by that?

If not then Thank you i will just flash my device with a stock rom