How to restore jailbroken iPhone on iOS 8.3 back to iOS 8.3?

I'm currently on ios 8.3, jailbroken, and i would like to restore my iphone, but with the new ios 8.4 update, it won't let me restore it back to ios 8.3, it will only let me restore and upgrade to ios 8.4. How would i go about restoring my iphone to ios 8.3 safely?

My iPhone keeps skipping a certain song on my playlist?

I have the iPhone 5s and it's completely updated. I have a playlist full of Fall Out Boy songs and whenever "Favorite Record" plays, it goes about 20 seconds in then stops and goes to the next song on the playlist. I don't know if I have to delete the song and redownload it, or what, but can someone give me any ideas?

I dropped my iphone 6 in water? - 3

So last night i accidently dopped my phone in water and i took it out dried it a little bit and left over night in rice i tried turning it on this morning and it said it needed charge but i'm scared that if i charge it its going to burn lol should i go ahead and charge it and if it gets hot just unplug it?

Sync iPhone with another computer? (different apple id)?

My sister bought a new iPhone 6 and plugged it in to my imac, it synced with my itunes and apple id, now she tried to sync it with her computer and got a message saying it can't be synced if it's not with my imac. What can she do?

What can I do with my SIM card to get my pictures back?

I had an iPhone 4 with so many pictures on it but sadly my iPhone broke. I do have my SIM card. I wanted to know is it possible to put my SIM card to another iPhone 4 and get all my pictures back. All I want is to get my pictures and send them to my email. Or is there anything that I can do with the SIM that can give me the opportunity to get my pictures and send them to my email?

My iPhone 4s Won't Turn On Past Apple Logo?

Okay, so the other day, my phone was low and it died. Later on, I put it on charge and after a while it began booting up, as normal. It displayed the Apple Logo for like 2 minutes, and then just cut out. I thought that was weird, but just assumed that maybe I'd knocked the power cable when I picked it up. I took out the cable and put it back in, and it began turning on immediately. Again, for about 2 minutes, it displayed the Apple Logo, then cut out. I tried it multiple times, but it just did the same again and again. I did all the different ways of turning it on and stuff, nothing worked. I tried using a different charger, still the same result. I took it to a shop and they replaced the battery with one I'd bought earlier that year, still wouldn't turn on. They replaced the battery with one of theirs. STILL wouldn't turn on. They tried 'flashing' it, but when I came back the next day, again, nothing. I'm getting really frustrated because my phone is simply a part of my daily routine, and it's important. I don't have the money to buy a new one, and won't for literally at least a year. (I pay for all my things with pocket money, £12 a week). My phone isn't on contract, I bought it refurbished and it's on Pay As You Go. I don't know what else I can do. Please help! Any suggestions at all will be appreciated, Thanks.
One more thing, my phone up to this point has been in immaculate condition. It's never been dropped, had water damage, or endured any other form of mistreatment.