Hello
I don't know the V145 model, but I have removed quite a few (about 40) IBM/Lenovo Thinkpads myself, mostly the hard drives and the main memory.
- If you have to break a seal, the warranty will probably be void (I have never had this happen with a Lenovo laptop).
- In any case, download the service manual for your model. There you will find information on how to open the case and which parts are replaceable (FRU = Field Replaceable Unit). There are models with soldered RAMs where this is not possible.
- Disconnect the laptop from the mains and remove/deactivate the batteries.
- then remove the RAM as described in the manual and insert a larger module.
- Keep the removed RAM. If something should break later, reinstall the old RAM and then send it in in its original condition for warranty.

Hello!
Actually, it depends on how you bought this laptop. Usually, "off-the-shelf" PCs, i.e. those you buy directly pre-configured from a dealer, have a seal. The warranty claim is lost when opened by the end user. Only repair by a specialist company in the event of a warranty claim is covered.
I myself only upgrade my PC if the warranty for the product has expired in its entirety. The advantage of Digitec is that you have a guarantee/warranty of varying duration on the individual components. If a part does not work as you expect, you can exchange it.

I recommend that you weigh this up, if necessary, not only to replace 4Gb but to upgrade directly to the maximum possible RAM capacity.