Well i installed CPU-Z to check what time of memory i have installed in this sistem and this is what i've found

https://www.runonpc.com/4atf51264az-2g3e1-driver-downloads-update/

Seems it's a DIMM memory

Also do i need to change the memory again if i upgrade to a i5-7500?

No, you do not need to change memory when you upgrade cpu.

you currently have installed Micron 4GB PC4-2400 DDR4 288-Pin Desktop Dimm Memory Module Mfr P/N MTA4ATF51264AZ-2G3B1

It is DDR4-2400T.  The T suffix at the end means it meets a specific JEDEC standard. A 2400T module will have the standard clock rates for a PC-2400 stick, and has a timing of 17-17-17, and a CAS latency of 14.16(ns).

Dell oem 16GB DDR4 includes Micron such as 

MTA16ATF2G64AZ-2G3B1 Micron 16GB PC4-19200 DDR4-2400MHz non-ECC Unbuffered CL17 288-Pin DIMM 1.2V Dual Rank Memory Module

It's A4 not MT and it's doesn't say what memory it is... searched the serial and part number and i get different results.I'm really confused atm

Sorry for not understanding these types of memory, was thinking i could upgrade the ram like all the ordinary PC's out there but i guess i was a little wrong about this. Found the official Micron website that says it has memory modules for the 3050MT should that be Okay?

https://www.crucial.com/compatible-upgrade-for/dell/optiplex-3050-tower

no need to get confused.  your CPUZ says Micron 4ATF51264AZ-2G3E1.

the complete Micro part number is MTA4ATF51264HZ-2G3E1.

DDR4-2400T PC4-19200

I am not sure.  If they accept full money back if not working, you can give it a try.  I would only choose and try those crucial memory that are DDR4-2400.

Would this stick work ?! Found it on my local platform...beside i know most people use Ebay and Amazon but when you live in East Europe and a memory stick cost 31$ and shipping is 49$ that's pretty bad

Well after doing some research... i think the best case scenario i'll just this 3050MT as a office PC and that's about it. What are some decent GPU that i could use on this with the standard OEM power supply that won't cause any trouble?

Re: Dell snpm0vw4c/8g memory

it should work

for office PC, no gaming, and 250w stock psu, you can use gt 730 (gddr5) or gt 1030 if you want a discrete video card.

gtx 1050 would be a stretch.  it will run with 250w psu in typical real world scenario but recommended psu is 300w.

brad (aka the OptiPlex afficionado) has brought up a good point which allows some more detail.  you can consider use the lower power gpu for Optiplex 3080 and Optiplex 3090 for your 3050.  some of the oem gpu such as RX 640 (2019) are newer than R7 450 (2016).

AMD Radeon™ RX 640, 4 GB, GDDR5 (optional, Tower and Small Form Factor only)

on the other hand, benchmark test seems to show that the R7 450 card is comparable to GT 1030, while RX 640 falls behind GT 1030.

note the 3080/3090 psu is 260w (MT) and 200w(SFF).  therefore, not much better than that of 3050.