I need to replace the original internal SSD (256GB) with a 512GB that has Time Machine on it and up to date.

I am hoping it were not required to involve yet a third disk - e.g. another USB hard drive in this process .. but am not clear on it. Let us call this 1TBdrive

Specifically it seems one solution would be:

• attach the 1TB hard drive and make it the time machine backup.
• power off the MBPro and physically swap the 256GB with the 512GB
• attach the 1TB USB hard drive and boot up, keeping the option button pressed to induce booting to time machine
• restore from 1TB TM to the new 512GB internal drive

Unfortunately I do not possess this 1TB external drive. So is there any way to do this with just the first two SSD's?

I need to replace the original internal SSD (256GB) with a 512GB that has Time Machine on it and up to date.

I am hoping it were not required to involve yet a third disk - e.g. another USB hard drive in this process .. but am not clear on it. Let us call this 1TBdrive

Specifically it seems one solution would be:

• attach the 1TB hard drive and make it the time machine backup.
• power off the MBPro and physically swap the 256GB with the 512GB
• attach the 1TB USB hard drive and boot up, keeping the option button pressed to induce booting to time machine
• restore from 1TB TM to the new 512GB internal drive

Unfortunately I do not possess this 1TB external drive. So is there any way to do this with just the first two SSD's?

UPDATE Here is the relevant available disk space info

df -k

Filesystem                        1024-blocks      Used Available Capacity  iused    ifree %iused  Mounted on
/dev/disk1                          243915264 235014420   8644844    97% 58817603  2161211   96%   /
/dev/disk7s2                        499771696 214002444 285769252    43% 53500609 71442313   43%   /Volumes/os2mellyrn

Notice the externally attached SSD used for TM (disk7s2) still has 280GB available = more than twice the internal (active) SSD (disk1)