Remapping layers in QGIS project to other folders?

You have a great plugin named "ChangeDataSource", doing just that very easily. The only downside is that you can only do one layer at a time.

Works on any layer type, including database layers, raster, wms, wfs, etc.

ChangeDataSource

Right click on layer tree to change single layer datasource of click on icon to change datasources globally

The plugin allows to change the datasources of the loaded layers. The operation can be performed right clicking on legend items for single layer or globally on a summary table by clicking on toolbar plugin icon. The plugin takes control of bad layers handling allowing to specify valid datasources working on project

See also :

• For more layer at a time, see @JGH answer.
• Handling bad layers : Updating file locations in QGIS projects?

ADDITIONAL INFO ON RELATIVE AND ABSOLUTE PATHS

QGIS will like to have all it's data close to its project...

the '.' string means "the folder the .qgs is in. the '..' string means "the folder up from where the project qgs is.

example :

• if you have a //NETWORK/WORK directory where your qgs is saved (i.e //NETWORK/WORK/myproject.qgs), you can use ./subfolder/mylayer.shp (relative path) to point out to //NETWORK/WORK/subfolder/mylayer.shp (absolute path) which makes your project movable.
• you can use ../otherfolder/mylayer.shp (relative path) to point out to //NETWORK/otherfolder/mylayer.shp (absolute path).

This way, you'll make your project movable, as long as your data is positionned in the right relative place. You can set this behaviour as default in the project properties (Project Menu).

Réf. Saving project with data source path as relative in QGIS?

you can open the qgs project file in your favorite text editor and do a search/replace with the old/new path.