is it possible to clone my running Windows 7 from a bigger SSD to a smaller SSD.
or do i need to reinstall everything?
Yes, it is certainly possible.
You might be able to do that using PartedMagic, but this is going to be hit or miss.
There is another option. When I purchased my SSD, I also got great Data Transfer Kit for free - this is basically USB/SATA adapter with bootable CD for copying data from one drive to another. Later I found that it can be purchased separately for about $15. This software allows to copy Windows to smaller or bigger drive and automatically resize partitions as necessary.
Any of the cloning programs can send the "clone" to a partition that is large enough to hold the data. Most of the cloning programs will tell you how much data is on the disk. Most of the cloning programs will tell you if a direct clone is likely to work (fit) on the source.
Cloning programs will often be set to Ignore (or have exception for) paging, hibernation, and unnessisary hidden File system file items. Making the data size a bit smaller. Some applications of cloning, will be "deleting" the partition prior to putting a Full Backup on the partition. Read what it is going to do carefully. It is good to have your disks Named, with labels, not just letters. (letters in NT systems are assigned)
1) Backup I would recommend making a "backup" of the partition, have the backup be an "image" file, which can be stored as a regular file.
A) Store this backup file on a hard drive , like one of your normal data drives that you use. Alternativly clone programs can store to CD or even DVD.
B) Prefer to use "compression" when making "image" files, because the OS files themselves will compress a lot. Already compressed User data will not compress.
C) Verify the backup, which just checks to see if it is written and valid.
2) Restore Now that you have a backup, anything could go wrong, and you can get back to the backup, and fix anything.
A) Set to verify the data (again) as the option to restore.
B) While the data is still on the original SSD , restore the backup, or direct clone (disk to disk) the data to the 2nd SSD
3) User Data: Here I do not concider "user Data" to be a part of the system disk, so any user data on a system disk would be copied without any special cloning methods, to any sort of backup.
By preserving user data seperate, the clones can be much smaller and quick to recover.
If your disk is too full to fit on the smaller disk, think about collecing the user data, or the larger user data, and storing it seperate. Video Files, Pictures, Music, Documents, and even the whole of the E-Mail folder.
Use whatever clone program acronis being my favorite this week. XXclone can also copy the files and setup the booting. might be an interesting way to do it. A good clone backup is better than system restore, and other system save methods that do not always work for all problems.
For a shopping list of free clone tools see Free way to clone HDD to SSD?
Side Notes: When you THINK you have a backup, and start deleting things , that is when things go badly.