If you think. I could get something better let me know.
I live in Australia. Also my budget to upgrade is about $300. Also I do not have any local places to get my computer checked out. I would also like to buy from https://www.jw.com.au. I also don't mine buying from ebay or stores in australia
In your shoes for a trouble free upgrade i'd move to a newer mid tower case with at least 2-3 120mm fans for intake/exhaust? These OEM casings have very limited ventilation and to be fair they are meant for home/office use not gaming?
If u have never disassembled a pc before there are videos u can watch that may help but basically just with a screwdriver you can do it all ^^ The important thing is to spot where the motherboard is screwed to the standoffs on the case