Hi @iridi ,
It does not have a M.2 slot but according to the [https://thinkpads.com/support/hmm/hmm_pdf/e330_e335_hmm_en_0b48602_04.pdf|service manual] it has a PCIe slot for either a half mini WAN card '''''OR''''' a mSATA SSD.
Go to p.63 in the service manual to view how to remove / replace the component.
The manual also mentions the following regarding the mSATA :
''If the computer is equipped with both a hard disk drive and an mSATA solid-state drive, do not use the mSATA solid-state drive as a bootable device. The mSATA solid-state drive is designed and developed for “cache” function purpose only.''
''If the computer is shipped with both an mSATA solid-state drive and a hard disk drive, the mSATA solid-state drive is used for the “cache” function and to support the Intel® Rapid Start Technology. We recommend that users do not replace the mSATA solid-state drive by themselves. Otherwise, the “cache” function will not work and the Intel Rapid Start Technology cannot be used any more. Attention: Ensure that you partition the mSATA solid-state drive after installing it on the computer you are servicing. Otherwise, the mSATA solid-state drive will not function correctly. For instructions on how to partition an mSATA solid-state drive, go to'' http://www.lenovo.com/support/msata-fru.